If you use feature branches, it is quite annoying that can't push two consecutive commits because CI changed something in your branch and now you have to resolve conflicts.
We have it set up to only run after you've opened a PR. You shouldn't run into the issue often that way because if you're opening a PR then all your big immediate changes are already committed so you won't be pushing another commit until someone reviews which will be after black has already finished.
Sometimes I still sneak in minor changes after I opened a PR. Sometimes I open PR early because CI has integration/e2e tests that are hard to run locally. Sometimes I want feedback on certain parts early on and PR is the easiest way to show something.
There can be workflows in which pushing through CI works fine, but as a general advice it's not great because there are many edge cases.