I calculate the real, diminishing value of my continuing to work frequently. It's pretty encouraging!
My first year of tracking was of infinite value, as my net worth went positive and established a FIRE date from none.
My second year I got a large raise, and substantially accelerated FIRE.
My third year I got another large raise! Again accelerated FIRE, but much less so proportionately, and a some of the advance in savings came from ROI.
And so on.
Once you're at 60%, you're moving the needle substantially less than the needle moves itself, which is awesome! Doing anything at all I enjoy, for peanuts, is vastly preferable to me over getting a moneyhose for work I hate, but I don't want to pay for it with 30 years of financial stress. The reason I'm interested in FIRE is to scale back and be able to focus on a future family and more enjoyable work. My most lucrative career prospects are just not what I want to do at all, so I frequently check the FIRE-value of this year's work vs last year's.