My experiences might be somewhat different than what you're thinking about because I took a couple of "working" sabbaticals (although each one had some long vacation tacked on to the end of it).
1. What prompted your sabbatical?
A. London, UK (mid-2001 to mid-2002): My then-boyfriend was a professor in Toronto and was planning a one-year academic sabbatical in London. He asked if I wanted to go with him. I hadn't really thought about it before but decided that it would be interesting to work in another country for a year, if I could manage it.
B. Paris, France (mid-2005 to mid-2007): My fiance (not the "then-boyfriend" mentioned above) and I decided that we wanted to pursue at least one more work-abroad adventure before factors such as aging parents limited our mobility. (He'd lived and worked Egypt, the UK and the US before. I'd lived and worked in the US and UK before.) So we looked for contract opportunities and I landed an amazing job at an international organization in Paris.
You didn't ask this question but people might be wondering if these sabbaticals felt like a break or respite from my regular job. The answer is Yes for Sabbatical A and mostly No for Sabbatical B. The job I left to do Sabbatical A was fairly high-stress, I had a managerial position, my regular working hours were about 45-48 hours a week (with much more intense periods arising unexpectedly every 5-8 weeks. The Sabbatical A job was, by contrast, a specialist / non-managerial position in an organization where the standard work week was almost always 35-40 hours (except in the immediate aftermath of 9/11, see below). However, I left a fairly relaxing and super-fun job (usually 38-42 hours a week) in Canada for a demanding role in Sabbatical B. Although I went from a managerial position (in my home country) to a specialist position (in Sabbatical B), in reality the expectations were higher, the hours were really long for the first year (long working travel days, lots of weekend work etc, there was limited support, and the work culture was mostly terrible. (Except for the fact that we stopped work at least once every couple of weeks to eat treats and celebrate something with champagne :) ) In the second year, when I was feeling somewhat unmotivated (and my major project was complete), I cut back my hours to a more regular 35-38 per week.
2. How long did you originally plan to take? How long did you actually end up taking?
A. One year planned. I ended up being gone for 15 months. I worked for exactly a year, and took a 10-week vacation at the end of it (plus I took two-weeks before my UK contract started to get settled).
B. Two years, with a possibility of extension planned. Two years plus 10 weeks. (I hated the organization I ended up working for, so I decided not to renew my contract. We took a 10-week break at the end for holidays and to relocate.
3. How did it impact your FIRE plans?
A. I didn't have FIRE plans at the time. The sabbatical set back my savings/investment plans by probably 15-18 months' worth of tax-advantaged savings. I was getting a salary in the UK that was technically the equivalent of my Canadian salary but the cost of living was significantly higher; I probably experienced about a 1/3 drop in purchasing power. Also, I owned a condo and although I managed to rent it (with all my furniture and my cat!) to someone for 12 of the 15 months I was gone, I had to cover the remaining three months plus a portion of the carrying costs. I also splurged on some experiences (frequent travel to continental Europe, the 10-week holiday at the end, language study classes etc). I spent every penny I earned, plus about $5K of my savings and put some charges on my credit card. However, I received a "re-signing" bonus when I got back to my old job, which I used to pay off my credit card and repay the $5K I'd "borrowed" from myself.
B. I didn't have FIRE plans at the time. I was getting paid about what I'd made in Canada, when COL and some supplementary funds from the organization were taken into account. However, my husband was unable to find work in Paris, so we were reduced to one income. Also, we had rented out our house in Canada and the rental only covered about 90% of our costs. Overall, I'd say that the sabbatical didn't set my retirement savings plan "back" but we weren't able to save as much as we had before.
4. Where did you go?
A. Moved from Canada to the UK (London). Also spent 6 weeks in France and 4 weeks in Spain at the end of the working portion of the sabbatical, taking language immersion classes.
B. Moved from Canada to Paris.
5. How much did it cost you? How long did it take you to save up for it?
A. See above. In the year before I left for the sabbatical, I cut back on some spendy habits (like books, clothes, takeout meals etc).
B. Didn't really cost us anything. The international organization covered our moving costs to and from Paris (including flights etc) and also provided us with a lump sum (about 9000 euros) to cover transition costs. (That sounds like a lot but we needed a couple of thousand Euros for a damage deposit for the flat, we had to buy second-hand appliances for the flat, et).
6. Did you return to the job/industry you were in prior to your sabbatical? Or did you switch industries/careers?
A. I returned to the same organization (a government agency) but changed roles with a promotion. The role change was a direct result of my experience overseas.
B. I considered moving back to the same organization but explored some other options in different countries as well. We came close to moving to Norway! (but there was a significant risk my husband would have trouble finding work there). We ended up moving to New York City, where I got a good job offer and there were a lot of opportunities for my husband as well. (My job offer came from an organization that one of my former colleagues from Sabbatical A had joined. He introduced me to the hiring manager.) My new role was in a similar field (international regulatory affairs) to what I had been doing before and during Sabbatical B.
7. What was the biggest positive thing that came out of taking it? The biggest negative thing?
A. Positive: Sabbatical A completely changed the trajectory of my career. It exposed me to work in international regulatory affairs, and my work experience enabled me to land a great role back at my former organization when I returned from Sabbatical A. It also helped me get the position for Sabbatical B. After Sabbatical A, I got to travel the world, meet all kinds of interesting people, and have a meaningful impact on regulatory policy. During my sabbatical I also discovered that I loved learning foreign languages, and started to enjoy taking language immersion holidays. Aside from the fun of those experiences, my improved language skills were very helpful in my career. (My French language skills were a prerequisite for getting the Sabbatical B job.)
A. Negative: My second day of work at Canary Wharf in London was 9/11. It was incredibly disturbing and disconcerting to be living far away from home, and working in a place that many people thought might be a target for terrorist attacks. Because I was new to my job, I wasn't very helpful to my colleagues, who were working all hours to help keep the markets running in the rest of the world. I mostly brought people tea and bought them fresh socks for a few days. Also, my boyfriend and I split up a month after we moved. That was a bad and a good thing. I think the stress of living together in a shocked world, far away from friends and family, stressed our relationship. In the end, I was glad that we figured out sooner rather than later that we were unsuitable long-term partners.
B. Positive: We got to live in Paris for two years, right after we got married! It was like a honeymoon. We loved having people visit us, and we loved traveling in Europe and the Middle East. I also liked some of my colleagues and made some lasting friendships, and I got to work on some interesting projects (in Turkey and Latin America, for example, and travel there). We learned a lot about wine and got to drink a lot of affordable champagne. The job I got in the US (after Sabbatical B) was very highly paid (compared to my job in Canada), and we were able to save a lot during the 9 years I had it. I also got some great low-priced stock compensation (because I started the job at the beginning of the financial crisis), and the company stock ran up a fair bit before that job and I parted ways in 2016.
B. Negative: My mother got very sick about a year into our stay, and died after a short illness. It was devastating to live so far away (she was in British Columbia). I also hated the organizational culture, which sucked the joy out of many people and stressed them out. It didn't affect me as much but I definitely lost some motivation to do my job well. On the plus side, the organization had a great bereavement leave policy (and my manager, who was a jerk in many ways, was incredibly kind to me and supportive when my mother died).
Overall, I would say that the two sabbaticals had a good ROI from an FI perspective. I learned things, made contacts, was exposed to opportunities and had resume-building experiences that enabled me to land a very highly paid (and interesting / impactful) Megacorp job. Savings from that job are the foundation of our current FI status.
8. What was the biggest thing you learned while on sabbatical? What would you do differently if you were to do it all over again?
More details to come. One thing I would change is that I had an opportunity to buy back a year's pension credit for the 12-month period I was working in the UK. When I got home, my pockets were feeling empty and the cost to buy that year of pension credit seemed high, so I took a pass. In retrospect, I should have bitten the budget bullet and bought the credit.
9. Do you plan on doing another one?
Nope, retirement is on the horizon (2024). Although I could imagine the possibility of one or both of us doing some kind of short-term quasi-volunteer work experience in a developing country (maybe something where we got a modest stipend to cover travel or basic accommodation for a while).