Will an exhaust leak post cats cause power loss?

[Boxtaboy]

Just wondering if an exhaust leak after the cats would cause any power loss. Reason I ask this is because I've noticed a number of Cayman and 987S folks have been doing a mod to their factory exhausts to get more sound- as their exhaust is designed as a 2-can exhaust system with two crossover pipes from one can to the other, some have loosened the sleeve from the top crossover pipe and slided them over to allow a gap between the pipes up top, allowing exhaust to escape from there.

The sound is pretty amazing after this mod...I've driven a friend's car with this mod done, but I was wondering if this sorta muffler bypass causes power loss. As it is post cats, it shouldn't, right?