The big thing, IMO, is that it basically offloads the distractions from your phone to your wrist, and lets you choose to ignore many/most/all of them depending on what you're doing.
If you take pride in not owning a smartphone, or not owning anything but the most basic smartphone, or hardly ever using a phone, it simply isn't for you.
If you're like many people, and constantly either A) missing notifications or B) being distracted by notifications and having to fish around for your phone to answer whatever just came in, it's actually quite nice.
Tap tap. You know those taps are a text. Flick your wrist up: it's from your friend asking what's up. You're busy; your wrist goes down. That's it. Later on, your answer it. Tap tap, your SO is asking something. Dictate your response. Done. You get the point. It's also a better replacement device during certain situations - let's be honest, a lot of people text while they drive, we can't stop them apart from ticketing them whenever possible; I'd rather those people dictated to their wrist than put a big screen between their eyes and the road...
I don't use my phone in a manner where this would be necessary for me, but I do really see it. A lot of people are too distracted by their phone, this promises to be, if not a cure, at least part of one.