Sometimes a kill switch is added as a matter of convenience as well as safety.
Fully closing the throttle doesn't always shut off my MVVS 26cc gas engine which makes the transmitter's throttle cut feature ineffective. It may not stop even when pulling the throttle trim back until the servo buzzes while it "crunches" the carb throttle plate hard against the stop. This engine idles reliably at 1340 rpm and flipping the throttle cut will sometimes slow it to 990 rpm where it will keep running for over a minute. Bad linkage, poor tuning, really? Or, could it be that some carbs have that little notch at the edge of the throttle plate that prevents the air from being completely shut off?