I occasionally shut off the engine on my (fixed wing) aircraft using the MAG switch.
I do so to confirm that the MAG switch and the ‘P’ leads are working.
The small amount of fuel left beyond the manifold evaporates very quickly. (Whether that’s a good idea on other aircraft depends on the specific fuel system fitted to that specific engine and aircraft and NOT some ‘one-size-fits-all’ rule.)
However, there are some basic ‘one-size-fits-all’ rules. One of them is that everyone anywhere near a propeller on an aircraft should be told to treat it as “DEADLY AND DAMAGING. DO NOT TOUCH! DO NOT WALK THROUGH OR STAND IN ARC!”
Funny story about know-all engineers. All the plugs are out so how could a propeller possibly be dangerous? Someone connects the air pressure for a leak check, and the prop parts the engineer’s hair.
Even if the plugs and the cylinders are off, no one should be touching propellers. Moving the propeller on an engine that has the jugs off can damage the engine.