I'm trying to think what purpose the kill switch serves. Fall over and the bike shuts off. Heading toward a crash, I'm busy working the brakes and clutch. "Runaway" motor, if such a thing should happen? I guess maybe.
Over the past 35ish years I have been on bikes where the cable became frayed and the throttle stuck open.
This only happened once on a street bike (GS 750), but numerous times when I raced motocross.
When the throttle sticks open the last thing you want to do is take one of your two hands off the bars.
With the problems that some are facing with the newer electronic throttle systems, I would suggest that is a very good habit to create some muscle memory and use the kill switch all the time!