Many companies have branches or subsidiaries that buy and sell from one another. Customers want ability to create an AP bill or SO invoice where the 'customer/vendor' is another branch. When released, the transaction should automatically create the corresponding entry in the other branch (AP bill creates SO invoice, SO invoice creates AP bill).
Example: Company has wholesale and retail divisions. Wholesale purchases in bulk and inventories items. Retail branch/company enters AP bill or purchase order when ordering from wholesale division.
Example 2: Company has subsidiaries (created for tax purposes) where one purchases and manages inventory while the other distributes the inventory. The purchasing company adds value that is reflected in a markup that needs to be passed to the other branches. The markup can be different for different products.