For motor-only applications, the slower the engine speed, the bigger the motor needs to be. Large motors could be expensive and might not suit within the allowable envelope space of a credit card applicatoin. Using a gearbox with a smaller sized motor vitès bwat enables the unit to operate 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 pastries pass. Because this is definitely a fairly light load, you would not need the conveyor running at 5000 rpm. If it was, there would be pastries and cherry filling everywhere!