I always understood it to not only do as mentioned in emergency situations but also because leaving it on, without the the bike actually running (key on), continually excites the ignition coils. Without the points opening and closing to trigger the coils to release the captive charge, there is a possibility of burning up the coils. I have never had to use it in an emergency situation, but during maintenance and repairs I always make sure it is off when I keep the ignition on.