You can use it to activate parts of Exposé. It's kinda pointless, it was just a test to see whether it would be better to have hot keys, hot corners, or a bubble from memory... Thankfully Apple chose the first two by default but left the third there for people to play with. 🙂
If you're confident with Terminal (and you don't have to be very competent for this particular task), enable it and have a play. 🙂