I'm already loving my G Watch R, so I'm sure there are going to be several uses for the Apple Watch that people can't think of yet. For me, I have the weather radar as my default watch face, and have ambient display on 24/7 with the battery easily lasting all day. Just a quick glance at my wrist tells me the time, current weather, forecast, and shows the radar. Very useful for me, since I am outdoors a lot so without having to pull out my phone and open an app I can see at a glance and within a second I can see if there is any precipitation around me, the temperature over the next 12 hours, etc.
I'm sure the Apple Watch will have similar features. Not to mention the ability to view texts, e-mails, etc. That way when your phone goes off, just a quick glance at your watch is all it takes to see if it was an important message about an event you're heading to or just a junk e-mail.