BOVs allow the turbo to spin more freely after the throttle snaps shut during a gear change, so when you snap the throttle open again for next gear you will be on boost quicker. If you block it off the pressure build up between the shut throttle and the compressor will slow the turbo down considerably.
So, blocking off BOVs is for posers. If you don't have homosexual tendencies, and prefer to go fast, leave it as it is.