I have seen folks set safeties on guns in the rack - more as a prank, but as you mentioned, in a tournament, it is a lost bird. In a HD scenario, it could be a lost life.
I take it you shoot skeet, American or International. Your body creates a memory. With practice the swing becomes an automatic, the lead comes natural and unconciously you follow throug after pulling the triger. When something is practiced repeatedly you do things naturaly. Same with the safety. When shooting a competition the safety should be on at all times exept when you step in the station when it comes off. When you are done, safety on and you step out off the station. Same thing hunting. With practice engaging the safety becomes second nature.