Cross drilling give the rotor more surface area, which in turn helps the rotor cool down more quickly. Slots on the other hand gives the pads a way for the gases from the pads to escape. Also it shaves the pad surface as your braking, letting the contact surface of the rotor and pad to be fresh and help prevent hazing.
But here is the real deal with them.
Current pads do not release a gas. So slots for that purpose is deemed useless. Now I do get the slots to resuface the pads but its just a placebo effect for me (I just like looking cool)
The cross drills on the other hand may actually work. but the tradeoff is much worse. This is why I stay away from crossdrilled rotors and so should you guys. Cross drilled rotors are very prone to cracking. In fact one session at a track day is all it takes for them to really crack.
I am not saying none of the other rotors crack. In fact most my rotors crack because of the aggressive pads I use on the track. But Cross drilled rotors are just plain scary how easily they crack. Also just to get the information straight for you guys, neither crossdrilled or slotted rotors are made to save weight. The better more performance oriented crossdrilled rotors have double the number of veins inside the rotor to not only strengthen them, but also to further help with cooling, causing the rotor to be even heavier than the stock.
Hope this helps.
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