Hi
SAP is giving option to make One Common purchase order for different warehouse locations. This is useful if, Centralized purchase order system exists in an organization to get maximum % of discount or low price by making big purchase order.
for eg: Your company is having centralized warehouse and all branches are making purchase request or stock transfer request to this centrallized warehouse. So you can consolidate all these requirement and put PO to vendor in whcih you can mention delivery warhouse (in Row level warehouse field) as branch warehouse. So SAP will automatically cancel parent PO, and generate multiple open PO's for branches you selected in line level.
Regards
Unnikrishnan