I’m just wondering if there is any description of the active branches on github in order to know what the additional functionality might be - e.g. lamagcie, multi-external-editor, etc
Most of those branches have an associated pull request. These should provide the relevant description.
As for the other branches, any core developer can make one as they see fit. That’s never a good indication of the importance of the branch or any sort of implication for future changes.