I use these a lot. My favorite use case is templates, especially ones that were not initially planned in the architecture.

Let's say i have some entity like an "organization" that has data that spans several different tables. I want to use that organization as a "parent" in such a way where i can clone them to create new "child" organizations structured the same way they are. I also want to periodically be able to pull changes from the parent organization down into the child organization.

If the primary keys for all tables involved are UUIDs, I can accomplish this very easily by mapping all IDs in the relevant tables `id => uuid5(id, childOrgId)`. This can be done to all join tables, foreign keys, etc. The end result is a perfect "child" clone of the organization with all data relations still in place. This data can be refreshed from the parent organization any time simply by repeating the process.