Does anyone asking about the value of Fitbit data track their spending? What's the value of that? Why not just check your bank balance, which tells you if you're broke or not? Except of course we all know the value of it. Once you have the details, you can see what specifically caused any changes, get yourself back on track (watch your grocery bill, etc) or adapt your expectations if those changes are permanent/semi-permanent (e.g. if you get married, have a kid, they start daycare, you have to go on medication, etc). Maybe you adapt the former to balance out the latter. Whatever is going on, having the detailed information allows you to make better decisions to work toward your goal(s).
Maybe you're sufficiently established in your money habits that you don't budget, don't track in Mint or YNAB or on paper, you just check that your balances are doing what you expect. Maybe you're satisfied with your fitness and sleep habits and don't see a need for that data. That's fine. No one is trying to convince you to buy a Fitbit! Really! Enjoy not having one. But (some of) you are devaluing the choices of those who *do* find value in one, who find the information helps them make changes...whether by identifying patterns or by being a motivational force.
I have a Charge HR--all the trackers that didn't do heart rate seemed like glorified pedometers to me; I would probably get an off brand or $10 mechanical one of those, or just use my phone. A couple things I've noticed since using my Fitbit: I'm really sedentary when I work from home and it gets me down, so I've made a conscious effort to work a walk or run in on those days; sometimes, I'll do laps up and down stairs to meet my "floors" goal even though it's arbitrary; and when I feel really crappy going uphill on a hike or running, my heart rate is up there, and taking a break or slowing down helps me feel better and finish the activity (like a poster above, helps me recognize and accept when I might actually working too hard for my body and regulate so that I'm pushing myself a good amount). Could someone potentially have these insights without the help of a gadget? Certainly. But (a) *I* personally simply *wouldn't* have thought about things in quite the same way without the data in front of me and (b) we live in a society that teaches us to internalize and ignore our physical needs (sleep, movement, etc) for various other goals (work, school, caring for others, etc). Many of us are too accustomed to disregarding our body's cues that we are missing something (tiredness, bad moods, lack of focus, etc). Again, not true for *everybody,* and if you're in touch with yourself, that is fantastic and wonderful, move along. But what you see in this thread is many people saying "yes, this was of value to me" and some others saying "no it couldn't possibly have been." How can you possibly say that for someone else? About something you haven't even tried?
None of this is to say OP needs one or should get one, which I think depends as much on their income as the other factors mentioned. With an income of $100k+ a $20k debt can probably be gone in under a year (or you have much lower-hanging fruit than a $50-$100 gadget to reckon with...or kids). If you're trying to pay off the $20k making $35k, your budget probably needs to be a lot tighter and the cumulative effect of spending the $50-$100 at 8% (effectively, by spending on a Fitbit instead of paying off the debt) is much greater.