Allow a PO to start off as a material/equipment request that does not require the superintendent to select a vendor. From there the PM can approve and the purchasing manager can assign vendors to the various line items and create multiple POs off of one request.

It is useful because it creates an actual purchasing system. It is not realistic to believe the person who starts the PO will be the one to select the vendor. Realistically, someone is going to request materials/equipment, it is going to be approved by someone, and then another person will shop prices and buy the materials from various vendors. Technically this can be accomplished with WOs but there is not a workflow option for WOs, so you can't control who gives approval. Additionally, you'd need to create multiple POs from one WO rather than just assigning vendors to the line items of the material requesting and automatically creating multiple POs.