I must be missing a trick here, what problem are these devices trying to solve?

I go to bed and sleep, sometimes better than others. My heart still works after 64 years and long may it continue. I go to the gym and train hard, I run a couple of times/ week and push myself reasonably hard, my heart rate goes up but always comes down again. I use a Casio F91 to time runs, simply to know how long I’ve been out. When I return I take it off and go back to a proper watch.

Generating data might be interesting but is it really any use? Unless you have an underlying medical issue it seems pointless to me. If you’re a serious athlete training hard to achieve optimum performance maybe these things add value, but I seriously question how much good they do for the ordinary Joe.