I have been doing it for the 10 plus years on my boat and my pump is still stock and have had 0 issues
SRC 🚤💨
I thought the same thing...then I had my pump apart and measured the wear ring- ~.125", total slop, about .062" per side.
I went with an American Turbine AA impeller, from the Berk A2, and was set at .010"-.012" per side, from Berk specs, and about .018" front-to-rear (Original pump had 5 or 6 seasons on it, built by G.S. Marine)
The pump still turned 4900, (5K in good air), but the hole shot was ridiculous, and gained ~2 mph on top end. (It coulda been the Bimini top down, too)
And NO, I will not start it on the trailer, only in the water. (But, I built my pump, and know what's inside it.)
If the OP's pump is a WJ, with the plastic wear ring, I wouldn't start it out of the water either.
Golden Eagle's (YJ's) and Panthers don't seem to care. Most jet boats will drain backwards to the level of the (engine) water pump ports by gravity, unless it has a pressure regulator on the system, so less than a gallon of water in the engine, and the logs usually drain dry, or close to it.
Will it hurt it?...Probably not
Will it help it?...No
And with a Rockwell style driveline, I cannot (easily) disconnect the driveline/pump.
Just my $0.02
Dan'l