rowsc is right, it was initially done to let the gases escape from between the pad and the rotor. Modern brake pads don't create much gas, and thus it is not necessary. Porsche and Ferrari put them on their car simply for looks at this point although it's not necessary, it sells, and so they use it. As far as cooling, while increasing the surface area of the metal to cool it is useful, you lose heat capacity by drilling out the rotor and thus losing a decent amount of material. Yes they are lighter, but you do run the risk of cracking them, and if left unchecked, outright failure. Not worth the money, just go with standard rotors.

If you're roadracing and having trouble with brake fade, it's time for some bigger brakes. Plenty of options if you're driving a civic. :hi5: