I think you are referring to the "crosstalk" tube. This is about a 3/8" line that runs from the SC inlet plenum to the lower IC to lower manifold adapter. It is there (from the discussions on the boards) is that since the SC came with a very small MAF and restrictive TB. As the SC moves air there is a point that the SC tries to pull more air than what can pass through the inlet system without restriction.
As this happens the creation of low pressure area at the inlet and the high pressure area above the rotors cause a large differential pressure that pushes against the rotors with a downward force. Since the blowers output is not continuous (like a leaf blower) it's pulsed it beats on the bearings(this is also the reason for the distinct howl of a roots blower).
The tube is there to allow a small amount of air to enter the blower and keep it from cavitation.
On a stock car without extensive inlet mods leave it alone. If you have a car with a 75mm TB, high flow inlet plenum, and MAF then go for it.
Jeff
And on the byass valve they leak big time. you could probably pick up about 1psi if it sealed properly. I am trying to figure out how to make one using a valve (like an exhaust valve) for a proper seal. I have a bunch of different bypass valves but haven't really tested them to see how bad they leak.
The Bosch valve used on Saab's and some others (Vortech uses one of these in their kit), I have been told leak at about 8 psi but I haven't verified this. There is a replacment unit that is aluminum instead of plastic. It's made by Forge, don't know if it's much better.