Briefly: you declare that you trust some npubs. Now you can also have an opinion on the npubs _they_ trust (and the ones they trust, etc.) - that is, you probably trust them *at least a little* also, since they are trusted by someone you trust.

Repeat this out a a few more hops and add a handful of other features (like context/tags) and you have a personal content algorithm, filter, community mute list, recommendation engine, and lots of other stuff. All decentralized, sovereign, subjective and portable.