Registering your trademark with Customs and Border Patrol (CBP) allows CBP agents to act as a gatekeeper, by allowing them to directly stop the import of infringing goods into the United States at the border.
Once you receive your trademark registration on the principal register, you are eligible to register your mark with CBP. After registration, CBP will check imported good for potential infringement of your trademarks and will seize those goods at the border, without any further action taken by you or your company.
You have worked hard to ensure that your mark and brand is uniquely associated with you, registering with CBP is a one-time fee which allows the CBP agents to do the enforcement work for you.