Standard servos will turn the arm with the spring attached, and it makes a nice safety mechanism should a servo fail, it will at least naturally 'try' to return to idle or off. If you remove the spring completely, you are taking that side pressure off the throttle plate shaft, and thus, with vibration the plate could then rattle in the bore, and eventually open it to a point where it no longer fully closes....etc. If you feel you must disconnect the spring from the arm, do leave it in place.