How could fluid retention be useable in any way? It is only a build up of water above the Tunica so any expansion would be purely temporary. The most important thing in pumping is time is not wasted on water retention. Shorter sets with counter measures between, using jelq style exercises is the best way to gain, tissue wise and keep fluid at bay. SRT gives a great routine of 5x5x3 which is, for most men, the best way to pump.