hybwrx2002

I've got a turbosmart veeport dump valve on my 02 wrx, it's got one of these twisty tops so you can make it harder/softer. Anyone have a clue as to what this actually does to the car performance wise? Surely if it's on the hardest setting the excess boost must go somewhere? back down to the turbo like the original dv? what about soft setting, would that be better?

Also if I drive along then let off the gas without clutching, it makes the nice birdy cheep noise, but if i do the same while changing up a gear there's no sound at all and the car lurches a bit?