This makes testing changes easier in other ways too: when I make experimental changes, I'm reluctant to commit them until I know they're working, since I like b

This makes testing changes easier in other ways too: when I make experimental changes, I'm reluctant to commit them until I know they're working, since I like being able to checkout an old commit and know it boots. In practice this means I end up with a dirty checkout, and uncertainty on which changes have been tested. In theory I could manage this with git rebasing and/or tagging, but in practice I lose confidence in whether I've accurately tracked. With specialisations, I'd comfortably commit an experimental change to my canary track, even though it might break, safe in the knowledge that the stable track continues to boot.