An approved LPO commits the company to the cost before the goods or services arrive. That makes it the basis of committed-cost reporting: what a project has already promised to spend, not only what it has been billed.
The LPO is then matched to the goods received note (GRN) and to the supplier's invoice before payment.
How Civova handles it
Civova raises purchase orders with an approval step; approved order lines charged to a project count as committed cost until they are received, and orders are matched to receipts and supplier invoices.