The video simulates how the glasses might be able to take over nearly everything your phone can do and more. For example, putting directions in your path to tell you where to go and sharing whatever you are seeing. Pretty cool stuff even if it isn't totally necessary.
I wear glasses already and I would love to have things like messages and what not come up on my glasses. It would save having to pull out my phone to check it and with voice dictation you could reply to messages very easily.
This is likely a long ways off if it ever comes about, but it is still interesting to think about a world where you don't have to use your phone to communicate and you can get directions projected in front of you while walking down the street or driving. Check out the video below it's very interesting. There are also pictures on the Google+ Page of what the glasses might look like.