The United States has entered into many free trade agreements that benefit both exporters and importers. In order to receive those benefits, exporters must certify that their products qualify with the provisions of those agreements. For example, when an exporter provides a NAFTA Certificate of Origin to their buyer, they are certifying that their goods qualify for reduced or free duty under the North American Free Trade (NAFTA) agreement.
When a shipment occurs within the United States, companies must realize that their domestic shipment may become international. When your domestic customer takes your products and sell them internationally as either a finished product or as a component of a larger product, they must provide their foreign buyer with country of origin information.