Yep, I usually shut if off and let the bike run long enough to empty the float bowl. I got in the habit when I had a CR500, always seemed to start a little easier with fresh fuel in the bowl.
Turning off the fuel and allowing the engine to stumble and die does not completely empty the bowl, but it's close enough and that's what I do at the end of the day. The only time my petcock's on is during the day's ride. It gets turned off at the end of the day and back on again at the beginning of the next day's ride. And as others have said, leaving the fuel on when towing/trailering a bike would cause the bowl to overflow, causing lost gas and probably a fire hazard too, and maybe contributing to a flooding condition? I use sta-bil only during the winter / infrequent riding season. QUESTION: Since petcock on = float bowl always full, wouldn't fuel constantly be evaporating and creating varnish and other deposits in the fuel system?