The pipe is the recirculating pipe and plumbs back air into the intake (just before the turbo compressor)..
I think what your mate might've meant was to de-snorkle the intake system. There is a resonator box that sits in the intake system before your filter
box whose purpose is to quieten down intake charge noise as well as the hiss from the turbo charger. Removing this also improves your intake flow by
a reasonable amount. This will make your turbo whine louder and make the 'woosh' from the factory recirc valve a bit more audible
However, if it really is the recirculating pipe you are removing, you will want to block this pipe or close it off.
It will make it louder, but the valve will sound quite s*** I will assume as its not a proper smoothed outlet
Probably not something I'd recommend..
Getting an aftermarket blowoff valve is all good as long as you block the recirculating hose off!
In terms of side-effects, it is said to cause your engine to run richer between gear changes. People have had different results.. some don't notice it,
some end up with mean backfire between changes..