One of the most useful cases for smart watches, for me personally, is sleep tracking.

My LG G and my Pebble before it integrate with the alarm app Sleep for Android. Basically, I set a "I need to wake up by X time" in the app, the app uses the sensors in the watch to monitor how heavily you're sleeping, and will actually set off the alarm at the point within ~a half hour before the alarm time where you're sleeping lightest.

For someone like me that has a very, very hard time getting up in the morning, it's a fairly life changing thing. I also have Sleep tied in with a set of Philips Hues in my bedroom to have it start ramping up the lights to wake me up.

I'm still not a morning person, but I'm less likely to sleep straight through my alarm in the morning these days.