Purpose of Changing Requirement Type by User processing Sales Order

Hi,

What could be the reasons for a user processing sales order to change requirement type in the sales order.......as we know that requirement tyor has only one requirement class assigned......so with the change of requirement type, requirement class also gets changed, which is essentially an object controlled by Production folks.....I want to undestand why has SAP given this option where in the user porocessing the document can change the requirememt type.....an you let me know possible scenarios.....

Thanks

Satish Talikota