The GRN is what proves a supplier delivered. It updates stock for store items and confirms the cost for direct deliveries to site, and it is one of the three documents checked before a supplier invoice is paid.
Short or damaged deliveries are recorded on the GRN, so the supplier is only paid for what was received.
How Civova handles it
Civova's goods receipts update stock at cost, create FIFO cost layers for store items, and recognise the cost of direct deliveries on the project they were bought for.