Say again
Quite right but you can tell if you've got a knackered magneto (I guess most of us check magnetos just before we switch off so we can do something about it before we go flying next, it's the same principle). I, for one, have also identified fouled plug(s) and cleared them(it) by leaning on the way to the fuel pumps. The point is that if you can identify something before you taxi anywhere it's got to be better than taxying to the hold and finding something during your power checks. And of course the power checks (which we all do don't we) are the acid test to show stuff up that you cannot see at idle.