What do you mean with "mob switch"?
A contraption to stop hostile mobs from spawning. We keep 141 withers in one bedrock cage and build a perma loader two chunks away to keep the hostile mobs - the 141 withers - in the lazy chunks constantly loaded to keep them added to the hostile mob cap, thus preventing new hostile mobs from spawning. We can switch it on and off with the perma loader, thus a mob switch.