A pallet arrives, the driver wants a signature, and somebody has to decide quickly whether the delivery matches the order. Counting boxes by hand and ticking lines on a printed purchase order is slow, and with forty similar cartons it is easy to tick the wrong line.
Mistakes found a week later are hard to claim. The supplier asks when you noticed, the paperwork has been filed, and nobody remembers whether three or four cartons of one item came in.
What helps is a quick, complete record of what was on the pallet, made while the delivery is still at the door, with the order data right next to it.