Queuing allows you to manage how many transfers will run at once: all run simultaneously, source by source, or per individual transfer.
Set the Transfer Queuing to Off, Single Source or Single Transfer
Off— All sources will be transferred at the same time. New transfers start while others are still running.
Single Source— Only transfers of a single source run simultaneously. When finished, the next source starts automatically.
Single Transfer— Transfers run one by one, even when from the same source.