The biggest benefit of wavy discs, and the reason they are fitted to some race bikes, is the lighter weight.
This reduces inertia and makes steering slightly easier.
The fact that they 'sweep' the brake pads is of questionable value, and it was recently proven by MCN that they are actually less efficient in pure stopping power terms than standard shaped discs.

Of course, the reason Gixxerboy fits them is that they look cool ;D

Jen.