As Ham said, it allows you to use far more fans, allowing use of lower flow and quieter fans. But as Ham also said it is still just ambient cooling, so in a totally perfect world where the conductivity of all bodies involved was perfect, it still wouldnt take idle temps on a processor producing 0.00000001 watts below that of the air moving through the radiator.
Water is, however, much better at handling high load and provides lower high end temps and reduces fluctuation on the way to that top end. Pretty difficult to have top watercooling performance and retain the volume advantage though.
Just ate 5 Cadbury's Double Deckers in 30 minutes