What is the difference between Autocreate and Auto create workflow?

Our current version: Oracle R12.2.6

Is there a difference or functionality limitations between Autocreate (where the user manually click on the Autocreate button) and Auto create workflow (where the CREATEPO workflow attributes are set)?

Why is a purchase requisition successfully auto created into a PO manually, but not auto created into a PO by workflow?

1. We capture a non-catalogue request (purchase requisition) in iProcurement without selecting an inventory item and without a BPA/CPA, entering all the required fields (i.e. category, price etc), supplier, supplier site (on which a Ship To/Bill To is defined) and suggested buyer. All this information is defaulted to the requisition line. After requisition approval, the user flags the checkbox for the requisition in the Requisitions page of the Buyer Work Center, selecting Add and Create. The PO then creates successfully and is submitted for approval without additional changes or capturing of data on the PO.