Believe it or not it is still frowned upon to pull your phone out in many situations. This allows you to just do a quick glance at your wrist and not have to take out your phone. I wear a watch every day, always have. Also when you're strolling through the crappy parts of the city it's a bad idea to have your phone out.
I am all for this. I bought a meta watch since the pebbles weren't out yet. It's a little weird at first but I find it very useful, especially at work. I can glance at my wrist and gauge from there whether or not that particular notification demands immediate attention or not. The watch battery lasts several days and the impact on the iPhone battery is minimal.
Watches are basically the only wearable electronic device that ever caught on. That's because they provided some absolutely critical information (the time) that is by its nature glanceable information. Watches were the most efficient way to take the time with you - what alternatives where there to watches?
Even then, lots of people didn't like them because they were wearable - if you leave it on all day, your arm can get sweaty and uncomfortable, it catches on your shirt sleeves, doesn't match your outfit, is too difficult to put on and remove, whatever. Lots of people never liked watches.
I also doubt that having a hunk of Apple strapped to your wrist is "safer" than an iPhone in your pocket. Firstly, I don't think an iPhone particularly (as opposed to any other branded smartphone) makes you more likely to be attacked. iPhones are rather common these days, even amongst the plebs. Secondly, it'll be easy enough to spot the guy following his wrist rather than his phone. This wouldn't be announced in a vacuum - the day after this thing is announced most people on the planet will have heard of it.
Peeking your phone from out of your pocket and tapping the unlock button can in many situations be even more discreet than looking at your watch.
The case for having something like this is pretty weak IMO. It's definitely not the first time somebody's thought of a super-watch that could make video calls or browse the web or whatever: none of them have caught on. They've all had cool, futuristic, hyped-up receptions and then flopped once people saw the price, how stupid they look, and the excruciatingly thin value proposition.