Just add to that, having the optical kill on the trainer switch allows you to sorta pulse the engine if you need too. I've seen a guy land like this. He also had a stuck throttle. It was running about 1/2 throttle and was stuck there. He lined up and used the spring loaded trainer switch to cut power to the engine, and then he would release the switch......... engine would catch and deliver power.......... then he would toggle the switch again and it would slow down the engine........... and he would let go and it would throttle up........ and then he'd toggle it again........... and so on.

He landed successfully without a scratch on the plane.