ATM achieves these features through the use of short, 53-byte cells. Long trains are very efficient from the perspective of the railroad company. A locomotive is needed whether the train has 1 car or 1000. . . . Longer trains reduce the percentage of overhead. On the other hand, if you are waiting at a railroad crossing, long trains can impose excessive delays.
Short trains allow users to cross the tracks more frequently.
For a given total number of freight cars, the average delay getting across the tracks will be approximately the same, over time, with either short or long trains. With long trains, most of the time no train blocks your path, but sometimes you must wait a long time for a train to pass. However, if the trains are shorter, the worst case delay will be less, since you never have to wait a long time for a train to pass. Thus, the variance of delay is reduced even if the average delay is the same. These applications need to transfer large blocks of data with a minimal amount of overhead.