I see a use case for a backup of just settings and CSS mods and such. The ability to make a backup before making sweeping changes to how a site appears, and being able to go back to the way it was before if all goes hopelessly pear shaped would be useful. But even here, some settings (eg “max post length”) may come back to bite you after the restore.
For testing/sandbox, I would have liked to be able to export just a subset of the posts, say 3 categories, and have the restore (on the sandbox) include the user accounts, settings, and content. There is an impex command in the CLI, but iirc that only included user accounts and posts.