On the ops desk the packing list is a source document for the rest of the file: the shipping instruction is cross-checked against it, and the weights that feed the VGM declaration are pulled from it. Customs officials use it as a reference to streamline clearance, and the receiving party uses it to verify the contents of each package and flag discrepancies or missing items. It is not the same as the commercial invoice, which states the value of the goods so customs can assess duties and taxes; the packing list records what is physically in each package, and that is what the cargo is counted and checked against on arrival.
Glossary
Packing List
The shipping document that itemises the physical contents of a shipment package by package: item descriptions, quantities, weights, dimensions, packaging details, handling instructions, and identification marks.