This feature was added to assist you when you receive a product different from the product ordered on an Advanced sales order (EP Sales order) it was primarily to allow changing of the pack size from 6 to 12 or vv as we found many of the producers would sell one product then send a different configuration.
Where the product singles per case are changing it will automatically half the quantity ordered and double the cost per case or double the quantity and half the case. It looks at the singles per case value and calculates based on the change.
The process is simple and quick but you have to carry out the changes one Purchase order at a time.
You give the form the new product code and when you save the PO and SO related to the order will be updated automatically.