The things that I can currently think of that I'd use a smartwatch for - 1) GPS / pedometer for running 2) music (without the need for a phone) while working out 3) discreetly checking notifications during meetings 4) navigation when riding a bike / motorcycle. I realize not everyone would value these and will say "JUST USE YOUR PHONE!", but for a $200 - $250 smart watch, I'd definitely drop down the money for these apps.
For running, the Apple Watch seems to add a heart rate sensor. Heart rate zone, timing for intervals etc could be very useful. I've already got a Polar V800 for this, but for many others this would be a great feature.