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Drilled holes and make rotors lighter all right, but they also introduce stress risers at every hole. What happens, then, if a rotor cracks, a section breaks out causing disaterous results. This happened to one of my late model stock cars, ending the race and causing a lot of damage. We drilled rotors before they were available from the manufactures. Braking definately improved.

What do drilled holes really do? Some ventilation is provided, but they allow gassing between the pad and rotor escape under extreme braking, reducing brake fade. Grooving accomplishes the same thing, but drilling takes it another step.

Drilling is not necessary unless you'll be subjecting your car to repeated heavy braking such as would be found under race conditions on a road course. Otherwise, they are to make your car look "cool".

If you drill your rotors, don't forget to chamfer the holes. Otherwise the rotor will act like a cheese grater working against the pads. You'll also have to have an accurate pattern laid out before drilling, then the rotors balanced as suggested. All things considered: If you want drilled rotors, buy them.