We like many organizations work with many local governments for events and training. Many of whom use Purchase orders for payment. I have setup the payment by check to bypass the need foe credit cards and an upload field for them to upload the purchase order document. In order to make this work properly it would be best to have the upload field be visible and required only when the dependent payment type field (payment by check for instance) is selected and require an uploaded document in order to avoid confusion. I am sure there are many other applicaitons for others based upon the same prcinicple.
