Very true...You don't 'have' to have one...But it could save you from an expensive runaway. What a fail-safe does is return your throttle to a preset position in the event of a signal loss.
It could be caused by out of range, outside interference, loss of power to transmitter from bumping it and a battery falls out...
Murphy's law dictates that that will only happen when the vehicle is pointing away from you and the last signal it received was FLOOR IT!!

I don't have one either, but it's on the list. I haven't had a runaway with this truck yet...