I am Deaf, so notifications (vibration) on my wrists are immensely useful. I can't hear the phone buzz or beep when my hearing aids are off.
I also have ADHD + ASD - Reminders/To Do alerts me to things I need to be doing, shopping list, task list, etc. and Timer lets me cope with time blindness by making me aware of the passage of time. It's now safe for me to play a quick 30m round of my favorite game. Calendar at a glance keeps appointments and daily events in front of mind.
I have 3 alarms set - one on my wrist, my bed shaker and my smart lights (I have a cycle that goes from blue-green-yellow that works effectively well in waking me without being harsh).
Activity tracking makes sure I get up every hour (Thanks a lot, time blindness) and move a little. I pair getting up with getting some water. Without which, I would probably sit at my desk and lose a whole day from it. I forget my vitamins always, so I have a medication alert for that.
I never remember to check the weather so having it on my wrist makes sure I always know what it's going to be like outside.
I am always forgetting my phone, so the LTE on my wrist lets me know if someone is trying to reach me (my closest knows to just simply ring me for the alert and then send messages).
It's tremendously useful and lets me appear to function like a normal person.