git-annex keeps track of in which repositories it last saw a file's content. This location tracking information is stored in the git-annex branch. Repositories record their UUID and the date when they get or drop a file's content.
This location tracking information is useful if you have multiple repositories, and not all are always accessible. For example, perhaps one is on a home file server, and you are away from home. Then git-annex can tell you what git remote it needs access to in order to get a file:
# git annex get myfile get myfile (not available) I was unable to access these remotes: home
Another way the location tracking comes in handy is if you put repositories on removable USB drives, that might be archived away offline in a safe place. In this sort of case, you probably don't have a git remotes configured for every USB drive. So git-annex may have to resort to talking about repository UUIDs. If you have previously used "git annex init" to attach descriptions to those repositories, it will include their descriptions to help you with finding them:
# git annex get myfile get myfile (not available) Try making some of these repositories available: c0a28e06-d7ef-11df-885c-775af44f8882 -- USB archive drive 1 e1938fee-d95b-11df-96cc-002170d25c55
In certain cases you may want to configure git-annex to [[trust]] that location tracking information is always correct for a repository.