This mentality came from guys who were not electricians to trade ie their title was Intruder alarm "engineer" I never understood it plus I was called out to a house where the guy could not trcace the supply to the alarm panel so he thought easy I will turn off the main switch pull the panel out then tape up the supply cable and tuck it under the floor and sort it out later . Well you know what happened next so when I got there I said you have blown the main DNO fuse and you were lucky you used insulated pliers. By this time the guy was in pieces as he said I was about to cut the cable with those old un-insulated pliers but thought I better use the insulated ones plus all he could say was "there was a hell of a flash and bang.