I know that the UUIUpdater Utility modifies a repositories UUID, but when you run the utility what exactly is it changing?
The repository UUID is incorporated into the SIDs of all repository trustees, and these are used to look up security information (entry access rights, privileges, etc.). The time-consuming part (as far as I know) is updating the access rights tables.
This is important because if you just modify the UUID in the database directly, you may encounter weird behavior with users appearing to have access rights but not actually having them applied, or the like.
It's a tool you can use when copying an existing repository. See: http://answers.laserfiche.com/questions/70284/How-to-best-duplicate-a-production-repository-for-use-as-a-test-environment
I am aware of what it is used for and I have read that thread. I am wanting to know what is it doing when you run it? It seems to take a while for it to complete depending on the size of the database, so what is it doing?