Governors can hide carb icing
Good point Draco - you are dead right, this is another potential shortcoming of relying on the governor.
So remember to monitor both RPM and MAP - if the manifold pressure is rising for no apparent reason that could be a clue something is wrong.
When I trained, governors had just been introduced and the system at that time was I was not allowed to use the governor until completing all my training: even the GFT was done with governor off.