It seems fairly standard practice at the end of a flight to switch mags off one-at-a-time to check each ignition circuit (i.e. Lycoming).
I always do it before shutting down (Lycoming) but only one at a time. One expects slight RPM drops to verify that the switch is grounding each mag. in turn. If the engine stops you have just detected a defective magneto.
I have had the engine stop when doing this at the end of the day after a flight. The magneto had failed and needed to be replaced. It meant that it was possible to get the aircraft fixed in a timely way and not find out about it only when starting the next time.
If it stops firing wnen one mag. is off then just let is stop.