Standard xTuple allows just a single purchasing authorization around the release (also known as posting) of purchase orders. There are no purchasing limits on what you can purchase, from whom and what your value purchasing limit might be. Furthermore, it is possible for anyone who can create a purchase order to print the order and send it to the external party thus creating a commitment against that external party.
The Purchasing Authorizations package adds comprehensive purchasing limits to the xTuple system and prevents the release and printing of purchase orders unless the user releasing the PO has sufficient authority based on several elements. Purchasing Authorizations are set up as a matrix of permissions and can be as specific or general as you desire.
Specific purchasing authorizations are known as purchasing levels.
