Smartphones were the latest computing evolution bringing general purpose computing with you all the time and with an incredibly ease to use interface. Now people are trying to introduce this new computing device (the smart watch). What does it bring?
It doesn't take up a hand since you don't have to hold it. You don't have to get it out of your pocket or turn it or pick it up to use it. To get it to do stuff you speak to it (possibly even easier to use than touch computing). It can be attached to your skin and read all sorts of data through your skin.
What it doesn't bring you is a sizable enough screen to view photos or text (yet). Also it doesn't take advantage of one of our most precise tools (our hands).
From this we may be able to predict what niches smart watches will evolve into to fill. Heavily voice based, quick call and respond style communications, updates and reminders, location based notifications, no-hand enhancers such as leveling, altimeters, etc... And since the watch is oriented towards your own face... it is heavily personal and can't be easily shared like a phone.