It gives maintainers and contributors the ability to “play in the same band” instead of being forced into “artist” and “audience” roles.
When you join Jazzband you will become a member of its GitHub organization and granted a wide range of privileges there such as pushing code to repositories, triaging issues, merging pull requests, etc.
You can leave administrative tasks to the roadies, the people making sure the band can play when they want.
Once you are a member you can transfer an existing repo to the Jazzband organization as long as you follow the guidelines. There are also many existing Jazzband projects which you can start contributing directly.