I use the sleep data for:
- personal research: I'm curious about my sleep cycles and sleep pattern - I know someone whose cycles are a beauty, mine are a mess. One can only dream...
- keeping track of insomniac nights and check if they coincide with other events (like migraines, intense exercise )
- checking if the kiddos had enough sleep, and let them sleep in (when possible). Lack of sleep => try to be extra gentle, take it easy for the day, plus off to bed early the next night.

I know the calories-out feature is not reliable, so I use it only as a loose guidance, but I want to calculate the calories-in (I discovered my protein intake was regularly between very low to low, so I adjusted that).

I like the map feature but hate taking the phone with me. I still take it when running or biking on new trails to check the distances and times it takes me, so that next time I know roughly how long it should take.

Have finally got one too and use it for the same purposes.
I like this new "toy", I find it very useful.