How many times have we hashed this over
One advantage to the cross drilled units is their ability to vent heat and gasses away from the surface area which has already been mentioned.
Will this make an impact in "street" driving? or a few highway stops? no, not really. But, in racing applications, managing HEAT of brakes is very important. When you are slowing the car down 10-20 times per lap for dozens to hundreds of laps, the amount of heat created can be extreme (1200-1500 degrees). Anything that helps lower this temp and allows the brakes to "last longer" at a higher efficency is worth doing. Hence their use on race cars. On street cars, it is more "marketing" to show a link between what is learned/used in racing and what can be used on the street.
In a pure "street" application, changing compounds of brake pads and tires (since this is what the brakes are "connected to") will have a greater impact in stopping distances than changing to slotted or drilled rotors, especially if they are the same size as the stock units.