Well it depends how bad its leaking. Leaking will send you rich. If its a minor leak, your ECU will read the front o2 sensor, adjust the fuel trims and bring you back to where you should be. But its no good for power. Otherwise wont hurt a thing.
If its bad, you can go too rich, and it all depends how rich. Could just slow you down, could slow you down and stink, could cause rich misfires or even bore wash (which leads to hosed rings and cyl walls.
What exactly are you hearing? Its virtually impossible to hear a bov leaking, so I am going to go out on a limb and say you arent. I have seen MANY cases where someone hears the sound of the turbo, and assumes its an air leak. Before I say that 100%, tell me EXACTLY what you are hearing, and what the conditions are when it starts and stops.