In a measuring instrument, the damping torque is necessary to bring the moving system to rest to indicate steady reflection in a reasonable short time.
Damping torque is an integral part in the measurement of moving systems because of its ability to control oscillation.
Damping torque is used to enable fast and accurate reading of an object that undergoes oscillation.
Although, as noted above there are certain methods of creating damping torque that are only applicable to a system if it meets the correct requirements.
Damping torque is a motion that isn't assigned numbers while being used, but rather is tested and observed using a pointer in an experiment.
Controlling torque on the other hand is generated by a measuring device, and thus is not a naturally occurring motion.
Finally, if it is critically damped, it has an equal amount of deflection and controlling torque, thus allowing the pointer to quickly find the correct value, without the system oscillating past that value.