ORIGINAL: RogerParrett
One might care about the difference, since torque is a component of velocity. If, for instance, you crowed the ailerons / flaps on a glider at a certain velocity during level flight, it would require a certain amount of servo torque.
However, if the glider decended rapidly with the servos still locked "on crow", the likely increased velocity would cause an increase of force on the control surfaces, which could overstress the servo(s). Perhaps "Holding Torque" helps one determine if that's possible.
But what do I know?... I'm in Marketing (with an engineering degree)... lol
Best... Roger
If the servos get overstressed at any point for any reason, you have the wrong servos. In the above case, you didn't choose servos that were strong enough, regardless of how they're rated. Also, since nobody really knows the force that different control surfaces really need, you can only estimate which servo to use and then try it out to see if it does the job.