Power (the stuff that gets things done) is torque times RPM. It is wise to pick the point where the RPM times torque is at a maximum. That speed point oftentimes is much higher than the intended load's RPM so "gears, belts & pulleys and chains & sprockets" match the motor to the load.
Your'e in a sports car with a manual 5-speed gearbox. Do you want to be in 1st gear or 5th gear when the light turns green? Same thing.