I just dont get this idea.

Unless... there is a valve right where the pipe splits into full system/cutout (read: to route the FULL exhaust volume to either the cutout OR the mufflers), is the exhaust not just flowing into both pipes even if its uncorked? Whats the point besides just making more noise? On a personal note, I think they sound terrible, unless you wanna sound like a rez-pickup truck. And they have to be hurting power on any GOOD system.