Use this setting when the front-end has a separate feeder belt in front of it. The feeder belt allows multiple books to be placed on it, and then feeds those to the actual inlet automatically. In this case the front-end is not allowed to reject any items, as that would conflict with the other items on the feeder belt and there is not likely to be anyone there to take the discarded book away. Selecting this setting makes the device never send any items back, even in "too fast" or "too many" cases.