Slotted discs offer increased durability under extreme conditions. They provide higher thermal capacity than a drilled rotor, which makes them a better setup in race like conditions. This is the more appropriate track setup as it constantly refreshes the pad and improves initial bite. You can also run more aggressive track oriented pads without the potential premature cracking seen with most holed discs. There are certain race pad materials that should not be used with a drilled disc.