PLUS!... now this IS a controversial topic...

If you vent to the atmosphere the ECU then thinks you have X amount of air and sends X amount of fuel to create the big bang but there is less air than there is supposed to be so every time you hit boost and change gear your engine will run a #OOPS#load richer just for that cycle, hence the reason why you see a "puff" of black smoke from a car that has an atmo BOV. Arguably this can lead to all sorts of problems...

But for the sake of the argument, if you plumb it back in AFTER the AFM (if you have one) than the correct amount of air is in the engine for the fuel.

Did that make sense? >.<