I have an Oura Ring 3 and I find it useful to:

* Track my sleep (ongoing, not just initially) - My sleep wasn't as good as I thought it was, so it's good to try and improve my sleep hygiene. I like seeing how much deep and REM sleep I got the night before and my blood oxygen levels. The app will advise to take it easy if it thinks your readiness isn't good, which is a good excuse to chill out :)

* Daily slovenliness tracker - it'll remind me to get up and have a move around if I've been sat still too long.

I've started resistance training recently and it's good to see the progress before any significant outward physical differences appear:

* Track my workouts

* Track activity - its figures are a little on the high side for calories burned, but if you treat it as a relative guide, then it's useful.

* Track recovery

* Track heart-rate and resting heart-rate

* Track heart-rate variability

* Measure VO2 Max

* Track stress - I always thought my intense periods of work were potentially stressful, turns out they're not and I rarely get stressed!

I pay no attention to the 'steps' figure, instead the app sets a daily goal - based on your readiness - with calories burned (or sometimes it'll tell you to have some downtime if your body temperature is high, or your sleep was poor, or your recovery wasn't good).

The long-term trends it tracks are just good to see, as one of the other commentators said: it's telemetry for you. The app is actually good. Which I don't say about many apps. It's certainly much, much better than the Apple Health app.

I don't consider the data to be super accurate (I haven't put it against any professional monitoring tech), it's all about relative changes to your vitals over time imho. I had no idea where my physiology was before, now I feel like I have a pretty good handle on it. As someone approaching 50 it's nice to confirm that I'm not dying yet ;)

I have pre-ordered an Oura Ring 4, even though the improvements seem relatively minimal, mostly because they're just useful enough and I buy into what they're doing and think they deserve to succeed.