What does the USPS primarily use Registered Mail to provide?

The primary use of Registered Mail by the USPS is to provide enhanced tracking and security for items sent through the mail. This service is specifically designed for sending valuable or sensitive items, which is why it includes features such as a unique tracking number that allows the sender and recipient to monitor the mail's status throughout its journey. Registered Mail also provides additional security measures, including limited access to the mail items during transit and a chain of custody that protects the contents.

These features make Registered Mail a reliable choice for important documents, valuable items, or anything that requires verified delivery. The added security protocols ensure that mail is handled with extra care, reducing the chances of loss or theft. This service stands in contrast to other mailing options that may prioritize speed or cost over security. Thus, the emphasis on enhanced tracking and security is a defining characteristic of Registered Mail, making it the correct answer.