Ok as soon as you let off the throttle to shift your throttle body closes. If your turbo is still spinning at that time(which it will be) where does the pressure go? It hits the throttle body and starts comming back to the turbo. This slows down the turbo almost instantly which "shocks" the turbo's shafts and bearings. A blow off valve(BOV) releases that pressure when your throttle body closes to keep from shock loading the turbo. It also helps you by letting the turbo slow down ALOT more slowly. So as soon as you drop the clutch in the next gear, your turbo is still spooled up instead of almost stopped. This helps you have a smoother transition between gears. BOV's are sooooo worth the money! I hope this helped you!