Wow!!!
I lose faith in the human race when I read these discussions.
Why would anyone want to chance damaging their engine or exhaust system by turning the ignition off at 1000 RPM and letting the fuel air mixture race into the system then turn the ignition back on just to see if there was a live mag?
Checking each mag separately will determine if there is a live mag....if you do not get a slight drop in RPM when turning off each mag separately then you obviously have a live mag.
If you are truly concerned that there may be a one in a million chance that there is a live mag and are determined to turn the switch to both off then do so at idle and allow the engine to stop......
Where do all these weird ideas come from?
Sort of reminds me of how many times I watch people lean out of their airplane doors and call " Clear Prop " and then hit the starter with a time frame so short that even super man would not have had time to move away from the prop had he been standing near it.
The monkey see monkey do mentality is truly at work in society.....and best observed by hanging around your local airport and observing the habits of a lot of pilots.