I think there is still a good value in having each student experiencing a knocked out warning lights situation at least once during the PPL training. Everybody is drilled to react to warning lights going on, but what if the warning lights are not working and you don't notice ? If you don't interpret a CHT gauge showing zero as a serious issue (after cross-checking by switching the Gov On/Off), then you might be in the comfort that everything is ok because no warning lights are shown, while the'yre just not working and you have no clue if there's really a problem or not.
For just testing the handling of Gov failures it would arguably be safer to unscrew the bulb (i.e. after preflight) and then pull the CB in flight so that the failure is not easily detected by the illuminated light.