Containers (ULDs) for handling baggage. Obviously only certain aircraft can use them (A319/A320 are the only aircraft currently in game that can use them).
Faster loading/unloading (on stand). The container can be loaded/unloaded away from the stand, potentially reducing the time the aircraft spends on stand.
Extra complexity (player challenge): an extra fleet (pallet loaders) on top of any belt loaders but can’t be used on all aircraft