Remember "Crazy Taxi"? In that popular arcade game, you'd have to drive around town, hailing rides and dropping off passengers, to earn as much money as possible within a time limit.
The most memorable part of that game, however, was that big green arrow at the top of the screen that would tell you where to drive, or turn.
Imagine seeing the equivalent of the big green arrow in real life.
Let's say you're visiting a city for the first time. You step out of the subway, but you have no idea how to get to your hotel. Since Apple's glasses are rumored to support Siri, maybe you just press a button on your glasses and ask for directions to the hotel. Suddenly, a virtual blue line appears that only you can see: It shows you where exactly you need to walk and turn, so you don't need to take out your phone every other minute and check the directions. Maybe your glasses show more pieces of information, like estimated time of arrival.