The purpose of the holes and the slots is to remove debris and gas that build between the pad and rotor, not for dissipating heat. The slots will not "cheesecutter" excess pad at all. The cracks that you sometimes see on drilled rotors is because the rotors where not broke in properly after install. There is a process you go through to keep from "shocking the metal" and is different depending on the manufacture and process should be included with the rotors.
with that said unless its a race car that heat there brakes to the point of glowing (like road racing)ultimately ineffective with other applications. They look cool though and I put them on my truck but no performance gain. IMO unless there bigger no better or worse then solid rotors which dissipate heat better.