Turbo doesn't like too much back pressure and that's a fact. If backpressure starts to rise equally with boost pressure and goes higher than boost pressure, that's a problem. It means more heat, more strain to the turbo and the engine and that's bad for power.

TTR has this kind of setup in their PV

http://race.ulkhyvlers.net/dragrace/Pite/060826/48.html

Ok it's a drag car but you get the point..