If you have staff that are out in the field and you need to purchase good for an emergency repair. Then they might not have time to go through a process of creating a purchase order and putting it in the system. Usually this is done on an agreement basis with a supplier for certain types or limited value. Which will allow the employee to get some supplies to make their repair. Now there are various ways the process could go from here but one of them could be that the employee comes back into the system and creates a PO and then uses a confirmation code to print a message on the purchase orders to confirm the goods they have already collected.
Here is a quick overview.
AX2012 R3 CU9