For motor-just applications, the slower the motor speed, the bigger the motor must be. Large motors could be expensive and might not match within the allowable envelope space of an application. Utilizing a gearbox with a smaller sized motor enables the unit to use at lower speeds.
To be able to understand the importance of using a gearbox to diminish motor speed, think about this scenario. You have a pastry conveyor that adds cherry filling as the speed gearbox pastries pass. Because this is usually a fairly light load, you’ll not need the conveyor operating at 5000 rpm. If it was, there will be pastries and cherry filling almost everywhere!