The spring pressure on the throttle servo is insignificant. If a servo is having problems operating the throttle on an engine I would look for linkage binding and not even consider the throttle spring to be an issue. As RCIGN noted, removal of the spring permits the butterfly to bang side to side and wear out the butterfly and the carb body. It does more good than harm to leave it there, so best to leave it unless you like trouble shooting carb issues after a month or so of flying. Also, some manufacturers have been known to instantly void a warranty if they find that the throttle spring has been removed.