CLEAR lets you skip to the front of the security line. You use a fingerprint for identification and even if you’re precheck you go ahead of everyone that’s waiting to have their ID checked.
Delta made an investment in CLEAR two years ago. That’s helped CLEAR to expand, and in turn Delta got their biometric technology which they’ve experimented with for aircraft boarding and for SkyClub access. In the future you should be able to check bags based on fingerprints rather than showing ID.