[weird-eye-issue]

This is an example where you don't need a UUID as the key (since you could have another field that stores this "secret" value), but it makes it very convenient if you do use UUID as primary key by default because you get that "secret" value for free (no need to create another column and index). In my projects I use it by default for all models. It comes in handy. Another use case is needing to know the primary key before inserting into the database (at either the front end or the backend, but typically the backend).

[tgv]

True, the record contains both a classical sequential id and a uuid (to maintain backwards compatability), but now everything is linked through the uuid instead of the id. Convenient, indeed. And there's never much data associated with a single uuid, so performance is not an issue.