Update Aug 2018 - This was released in Bitbucket Server/Data Center 5.13

Original description below:

With the fixed hierarchy of only two layers (Projects-Repositories) proper categorisation of repositories can become cumbersome.

This can greatly alleviate this in large organisations with many repositories.
Tags or Labels here are the same concept as "Labels" in Jira. This is not tags as in `git tag…`

In our use case, some things tags would be used for is specifying:

• development teams involved and/or responsible for a repository,
• primary technologies involved,
• primary systems components involved,
• status flags, etc