You can change reservations on sales orders if, for example:
Priorities on existing reservations should be reordered. Suppose an important customer places a large order with your company and requests immediate delivery. In this case, you might have to cancel some reservations to be able to deliver.
Deliveries are unfulfilled or canceled, and the inventory on-hand must be shared among customers who are waiting for goods.
If items were not reserved when a sales order was created because it was planned to be done manually later.