For motor-only applications, the slower the electric motor speed, the bigger the motor needs to be. Large motors could be expensive and might not fit within the 
allowable envelope space of a credit card applicatoin. Using a gearbox with a smaller sized motor allows the unit to use at lower speeds.
To be able to understand the importance of using a gearbox to speed gearbox decrease motor speed, consider this situation. You have a pastry conveyor that adds cherry filling as the pastries pass. Because this can be a reasonably light load, you’ll not need the conveyor running at 5000 rpm. If it was, there will be pastries and cherry filling almost everywhere!