It's one way of purging preservation fluids from an engine thats been in storage.
But its much better to purge the preserving oil by opening the LP fuel filter drain and turning on the boost pumps.
Wet cranking is used when a new engine is installed.
RR call it an "oil circulation and fuel drain test". You wet crank the engine until fuel comes out the jet pipe. Then check that the residual fuel drains from the engine via the drains system, and check the MCDs to see that oil has reached them. Then you start the engine for the first time.
To do a leak check on fuel components, you spray chalk dust on them, and run the engine at high power. Then open it up and check. You must use high pressure fuel, the fuel pressure at cranking speed is not enough.
I can't think of any reason to do it at other times than a new installation.