For motor-just applications, the slower the motor speed, the larger the motor must be. Large motors could be expensive and might not match within the allowable envelope space of an application. Using a gearbox with a smaller sized motor enables the unit to use at lower speeds.

In order to understand the need for using a gearbox to diminish motor speed, consider this situation. You possess a pastry conveyor that provides cherry filling as the speed gearbox pastries go by. Because this is a fairly light load, you would not want the conveyor operating at 5000 rpm. If it was, there will be pastries and cherry filling all over the place!