For me, the appeal of a smartwatch is as an alternative control and notification system.
I stopped wearing a watch 5 years before I got a cell phone, when I started carrying around a PDA. It's just much better at everything a dumbwatch can do, except for immediate access and battery life. Now I use a smartphone.
But a smartphone sucks. To interact with it, you enter the unlock code and then hunt down the app that you want to use. Taptaptaptaptap, swipe swipe, tap, wait which messenger app, tap, wait, tap... I'm getting repetitive stress injury from this thing.
Part of it is that Android sucks. I miss Maemo and its extensible chat program. But I imagine that I can decrease the pain by using a watch to unlock the phone, and to do other routine interactions.
With a little more independence and a lot more security, I think a watch could be pretty useful. For example, I hate carrying keys. It would be nice if I could do that watch-door-entry trick from the hotel, but at my home and work. I guess a lot of people like the heartrate/pedometer sensor thing, too.