Originally Posted by CargoDane

Well, some of us ride on roads where it is sometimes necessary to do so due to "stuff" on the road. Especially after a long period of dry followed by the first rain - "road film" in other words. Or in winter with various road slush and what have you. Hell, even hitting a bush can put oils on the rotors, and then "burning it in" for the rest of the trip.

Removing such things from your rotors makes your brakes work better. And you can never have too much stopping power (although you can have too little modulation).