Field help (DLVPIO) 

In this field, specify the delivery priority (Normal, Urgent, Very urgent). The priority is used to classify orders during the delivery preparations.
It is initialized by the customer delivery address. It is used on the order lines by default where it can be modified if the delivery method for the order is not Complete. If you modify this information and order lines already exist, the system will suggest that you apply this modification to the order lines.
This information is used in the automatic allocation processing of orders to determine the priority of the orders.

The order lines applying to non-deliverable products are not impacted by this information.