I would assume it's for on-the-fly generation of links. The example I can think of (which they're not actually using it for) would be for Google Maps, with it's

I would assume it's for on-the-fly generation of links. The example I can think of (which they're not actually using it for) would be for Google Maps, with it's horrible long URLs, give the user a g.co link when they ask for the link to share. They did actually used to do that (with goo.gl) but apparently have stopped, perhaps it is soon to be brought back under g.co But yeah, it's essentially the same as Twitter's t.co, except that not only does it have to have been created automatically by Google (like t,co), it also has to link directly to a page on Google's servers (unlike t.co). Thank God for Google owning YouTube, which ensures morons can still rick roll.