Gurezaemon:
In all seriousness, what do people use sleep tracking for? Am I missing something obvious?
Obviously apple watch shows you the length of time in each sleep stage, I'm a notoriously restless sleeper and its very interesting to see at what stage of the night my deep & REM sleep is compared to other nights. Sometimes as mentioned this can be affected by workouts/stress/alcohol/caffeine etc
More for me, some nights I can go to bed early yet don't benefit from a better sleep. The watch knows how many minutes you actually slept for compared to how long you were actually in bed. Two years ago I listened to a podcast on how important a minimum 8 hours were to the body so since then I have been focused on sleep quality and length in particular.
YMMV of course