The D Inventory Interface is required in order to maintain order integrity between both the Sales Order and Purchase Order. Downstream issues within the sales process can occur. For example, if your SD sales order is placed on hold, this hold is carried to the related purchase order. However, if using an Inventory Interface other than D (Y or N), releasing the sales order from Release Held Orders (P43070) application, will not release the hold on the related purchase order.
Full details and setup is in Direct Ship Orders (Doc ID 625588.1).