As an example, consider a person riding a bicycle, with the person acting like the motor. If that person tries to ride that bike up a steep hill in a gear that is created for low rpm, she or he will struggle as
they attempt to maintain their 
balance and achieve an rpm that may allow them to climb the hill. However, if they shift the bike’s gears right into a velocity that will create a higher rpm, the rider could have
a much easier time of it. A constant force could be applied with clean rotation being provided. The same logic applies for commercial applications that want lower speeds while keeping necessary
torque.
• Inertia coordinating. Today’s servo motors are producing more torque relative to frame size. That’s due to dense copper windings, light-weight materials, and high-energy magnets.
This creates greater inertial mismatches between servo motors and the loads they want to move. Utilizing a gearhead to better match the inertia of the engine to the inertia of the load allows for using a smaller engine and results in a far more responsive system that is simpler to tune. Again, that is attained through the gearhead’s ratio, where the reflected inertia of the load to the engine is decreased by 1/ratio2.
Recall that inertia may be the measure of an object’s level of resistance to improve in its movement and its own function of the object’s mass and shape. The higher an object’s inertia, the more torque is required to accelerate or decelerate the thing. This implies that when the load inertia is much larger than the electric motor inertia, sometimes it could cause extreme overshoot or boost settling times. Both circumstances can decrease production line throughput.
On the other hand, when the electric motor inertia is larger than the load inertia, the engine will need more power than is otherwise essential for the particular application. This raises costs since it servo gearbox requires having to pay more for a engine that’s bigger than necessary, and since the increased power intake requires higher operating costs. The solution is by using a gearhead to match the inertia of the motor to the inertia of the load.