I regularly read the git blog and release notes, but did not see mention of this new feature in either. I was pleasantly surprised when I saw this tweet from James Ide:

This may be minor as it saves only a few keystrokes. (Less than it seems, because --set-upstream can be abbreviated as -u.) But, I do it many times a day and almost always forget to do it the first time so I bet its impact will be significant. I see almost no reason not to do git config --global --add --bool push.autoSetupRemote true.

The git manual describes the option, and the use case is detailed in the original email and actual commit.

At the risk of repeating what James wrote, this is what happens before the feature was implemented.

moonstone:~/www.oasys.net/(main=)$ git --version
git version 2.36.1
hub version refs/heads/master
moonstone:~/www.oasys.net/(main=)$ git cob testautoremote
Switched to a new branch 'testautoremote'
moonstone:~/www.oasys.net/(testautoremote)$ git push
fatal: The current branch testautoremote has no upstream branch.
To push the current branch and set the remote as upstream, use

    git push --set-upstream origin testautoremote

After running brew update git, --set-upstream is no longer needed, and git does what is expected.

moonstone:~/www.oasys.net/(testautoremote)$ git --version
git version 2.37.0
hub version refs/heads/master
moonstone:~/www.oasys.net/(testautoremote)$ git push
Total 0 (delta 0), reused 0 (delta 0), pack-reused 0
remote:
remote: Create a pull request for 'testautoremote' on GitHub by visiting:
remote:      https://github.com/oasys/www.oasys.net/pull/new/testautoremote
remote:
To github.com:oasys/www.oasys.net.git
 * [new branch]      testautoremote -> testautoremote
branch 'testautoremote' set up to track 'origin/testautoremote'.

Here’s the relevant section of .gitconfig:

[push]
        default = simple
        autoSetupRemote = true