More than anything else, soaking them makes them a little less brittle so they last longer. Where you posted the links to the Sullivans brushes earlier in this thread was the first I'd ever heard of any being pre-soaked. We still use pure rice roots, but I'm sure the synthetic blend would be alright. There used to be a saying that you knew you were doing it right if you wore out a new rice root on every calf you showed. I've never dedicated one brush to one calf, so I can't say for sure I've done that, but we do go through them pretty steady.