anyone know if its safe to put a switch between coil and ground on battery(think thats where it goes)

a mate of mine put a hidden switch under the dash on my car which i think cut the ground to coil, so that when some numpty tried to steal my car it just kept turning over. rather than just cutting ignition which they knew to look for

is it safe to do this on AT as its a quick and easy way to stop(if they get round everything else)thieves starting the bike, or will it kill it?