This transition is from `git-annex sync` needing `--content` to send
content to repositories that have preferred content configured, to sending
content by default to such repositories.

There should be no change in behavior with repositories that don't have
preferred content configured. `sync` without `--content` won't populate them
since that would be a surprising thing and a warning based transition was
judged by the community to be not sufficient to avoid that possible large
surprise. (See [[bugs/Changing_sync_to_include_content_breaks_UX]])

A warning was added in August 2023 when it's run in a way that will change
behavior. It would be good to wait until all git-annex users have gotten
the version with the warning, and used it for a while, before finishing the
transition.