I agree that that sort of effect definitely has a place in D&D, the problem becomes when that kind of trick becomes what the game is balanced around. When it becomes punishing to not be observant and pull off those tricks, then it stops being a case of telling others to just not do it, because not doing it means not engaging in the game the way it's designed to be played, which if you have to suggest that, is indicative of a potential problem with the game.
