PO Module will allow you to send the PO to JC Commitments and update the "Qty on Order" in Inventory(IV). Once you receive the PO in the PO module, it will update the "Qty on Hand" in Inventory, and allow you to send the invoices to AP which includes updating the status of the commitment in JC, and creating entries in GL. We're not using Project Management so I don't know if PO & PM interact or if the other method you mentioned has different advantages. PO also allows you to setup Vendor Price Lists so you can create PO's at a set price per item (which you can also override by permission). You can order the items for specific jobs or for your general inventory. Since PO works well with Inventory, this is probably the biggest advantage.