It can dry the coils, and as wally or someone said, everyone does it differently, but much of the purpose is to burn off the gunk that's on the coil. If the wick is wet, like bad said, you have to dry burn longer since it has to dry the wick first. Then it can start to burn off juice that has caramelized and gotten caked onto the coil. Since it's burning off this stuff, that's why I always rinse mine after the dry burn, then just blot the wicks. If you fill it up while the wicks are damp, it only takes a draw or two to get the juice wicking again so you aren't vaping water really.
This is one I've been waitin on to try.
