The importance of a BOV, why it saves your turbo.

The BOV will vent the excess pressure when you back off to the atmosphere. This excess pressure otherwise would bounce off the shut throttle buterfly and back into the copressor wheel and produce a massive shock load.

If the engine has a BOV the turbo will have a more sustained life and the engine should have more durability and driveability.

I think that the Pssccchhhttt sound is great and if I had a turbo I would get a noisy BOV for the "wank" factor alone. But I very much doubt whether a BOV will give you a measureable power gain.