TRS does not have enough strength to close the carb if battery juice in your receiver is severed yet the linkage is attached to the servo. Try it. Turn your power off on your receiver at WOT and you will be lucky if it closes a quarter of the way.

If your battery power in your receiver becomes dangerously low, your servos become sluggish and slow to respond. If that happens (without a TRS) and you brake at WOT, it may take a full second or two before your carb closes and another second or two before the brakes start to slow down the truck! In racing, that means you missed the breaking zone after that long straightaway by about a mile and your truck jumped the banked corner and sailed clean into the 3rd row seating of the bleachers and RPMs are JUST starting to die down! That is why you need a TRS in racing! It helps close the carb in a timely manner. Same scenario WITH a TRS and you may have only over shot the corner and missed the apex and possibly drop back a position or two because some one passed you on the inside and was quicker on the throttle out of the corner! But I digress.

A TRS is to help assist the servo and return the carb to a closed position in a timely maner. In the UNLIKELY event that your linkage disconnects from the servo, the return spring will close the carb. Yes. However that is not what it is designed to do.