A shipment can be packed perfectly, invoiced correctly and collected on time, yet still be delayed or made unexpectedly expensive by a few digits on a customs declaration. That is the practical answer to why use commodity codes: they provide the common language by which customs authorities decide what goods are, what rules apply to them and what must be paid before they cross a border.
For British firms, this ceased to be a specialist concern confined to large freight departments when the UK left the EU customs union. Businesses that had long moved goods to continental customers with limited border formality found that classification had become part of ordinary commercial administration. The same is true for importers. A commodity code is not clerical decoration. It can affect the landed cost of a purchase, the documents a customer needs, the availability of a tariff preference and the likelihood of a consignment being stopped.