The only plus I see is you do get a pressurized flush of the valve assembly of the fill valve. Some of my inflators are 30+ years old, and still going strong. I'd like to think it played a part in their longevity... Maybe not....
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I bought one of those yellow things to put water in my BCD for after dive trips; it works, but is painfully slow to fill. I think slower than just holding the deflate button and running hose water in the way Eric Sedletzky described.