For wide bodied aircraft containers are the only way to load/unload efficiently. If you are having to take a bag off because the passenger hasn't made the flight or is offloaded for some reason it is very easy to locate which container their bag is in, and it is a lot faster to offload the container, even if it is in the positions furthest from the hold door, than it would be to offload and reload 300 bags and have to check the bag tag of each bag to find the one you want.
The LDL should remain in position until such time as the ramp despatcher has confirmed all is ok with the bags/freight. If the flight closes up and is held on stand for a long time and someone needs to get off and have their bags offloaded then it could be that the equipment has moved onto another flight.
A320 containerised a/c are very rare, most are bulk load to use the inplane system weight for payload, but only if the bag is in the doorway would it be faster than to unload the bags down the conveyor belt, check the labels and reload the bags that should travel up the conveyor and restack and re-net in the holds.