The biggest thing that my Pebble does is allow me to see messages without having to remove my iPhone from my pocket. I can be in a meeting, class, wherever. I see all my notifications that I've asked it to show me. Messages, emails, calls, app notifications. A quick glance at my wrist and I know what the message is. If I need to take my iPhone out and respond, I will otherwise, I just dismiss it.
Another neat feature is it lets me know that I've just left my iPhone behind. Silent alarms are a neat feature too. A quick little nudge to remind me that my calendar has an upcoming appointment.
Like I said, a smart watch isn't for everyone. Many won't want it. I'm looking forward to the Apple Watch for added functionality.