simulates the look of "toy" cameras like Holgas, for example.
Gives the look of expired film through plastic lenses on cheap bodies with light leaks and what not. It's like having the fun of shooting with a Holga without the cost of film and less waste since those cameras can be so inconsistent.
I think it's kind of fun on the iPhone, but I haven't really taken the time to do it with any of my real photos. Granted, I've been shooting sports primarily for the last six months or so, so it would be a bit inappropriate.
A lot of wedding photographers are into it right now, too. The vintage look is real popular right now for candid portraits and stuff like that.