Wilwood "Drag" REAR Drum to Disc conversion kit

Been looking at these :

Wilwood Disc Brakes 140-8853-D - Wilwood Forged Dynalite Rear Drag Brake Kits

http://www.summitracing.com/parts/WIL-140-8853-D/

My question is...why is it called "drag"?

Will the rotors wear too quickly in street use?...or is it just because its a lightweight conversion?