With Clear, which is a private identity verification company, you are escorted to the front of the Precheck line. Think of it as Private Precheck. I've been a member for awhile. The list of airports (and venues) where it is used is limited, but it can be a lifesaver in some busy airports.

Think leaving Las Vegas at the same time as a major convention ends, and when the lines, including Precheck, are huge. 200 people in the Precheck line, 2 in the Clear line, where do I sign up?

If you sign up for Clear you will quickly find out, in the enrollment process, how much of your personal information has been collected, going back more decades than you can imagine. (I don't fault Clear for that, they don't collect it, but it's their job to search it.) I was mildly shocked at all of the entities (local government in particular) who have sold my personal information over the years.