As I recall grooved rotors offer a couple advantages. One being that they provide a 'channel' for the gases to escape much like crossdrilled rotors direct the gas into the venting area. The other is they tend to keep the pads clean because the edges on the channels act like a knife scraping off crap that builds up on the pads. Those edges also give the brakes more 'bite' when you first step on the pedal because of the rough edge trying to grab the pad. Pardon all the scientific terms :rolleyes: but this is basically what I read on a site somewhere.
