When customers place large orders, comprised of several shipments, but they are not ready to set specific delivery dates or quantities, you need master orders.
Saving an order as a master, reserves the total quantity of items in inventory. When the customer confirms a specific delivery date and quantity, you generate an order to pull from the master reserve. Any of the ship to locations can pull from their company's reserve.
Plant Partnertm keeps track of all the orders generated from each master, the total quantity committed against each master reserve and the the quantity left in the master reserve to be scheduled.
You'll always know the total quantities committed in inventory for master reserves versus confirmed orders. As inventory gets tight, you'll know who to call to find out what can be freed from master reserves.