BOV from factory are for emissions. They also do alot of strange things, RB20DET's stock BOV actually leaks on purpose. All factory turbo cars will have a BOV, cause they will plumb back, just for emissions.
Compressor surge is bad, as it stalls the compressor wheel. Does take alot of PSI to kill one though (40+ lbs) So, someone running small boost I.E 7-12psi, wont have a drama with it. Unless, its a cheap chinese turbo. I have seen compressor surge kill a chinese made one, was indeed funny.
IMO, factory plumb backs > External gating. The noise is just wank.