What is the point of a purchase order?

The point of a purchase order is to put a purchase in writing before money moves: what you're buying, at what price, in what quantity, delivered when — approved by someone with the authority to spend. Once the supplier accepts it, both sides have the same agreed record, which is what prevents most buying disputes before they start.

In practice a PO does four jobs at once: it authorizes spend (no more mystery purchases), it locks the agreed price so the invoice can be checked against something, it gives receiving a checklist for what should actually arrive, and it creates the audit trail accountants and lenders ask for.

Small businesses often skip POs until the first pricing dispute or duplicate order — which is usually the moment the point becomes very clear.