Field help (DDLVPIO) 

This information (initialized by the delivery priorities in the Delivery tab) is used to specify the priority of each line. This information is used to prioritize the preparation of certain order lines. It is used in the automatic allocation processing of orders. It is possible to allocate orders by priority level (e.g. to supply all orders when the stock is insufficient).

SEEINFO If the delivery method for the order is Complete order, this information is not accessible at the order line level.