Let me take a shot at why it's important.
We spend years peering at code hunting for tiny, miniscule mistakes. Thus we're training ourselves, quite rigorously, to spot minor deviations.
We're also irrational in the moment: our aesthetic sense is bothered by certain patterns, and our social sense wants to assign blame for this "wrongness" to individuals.
An auto-formatter removes a ton of deviations that don't matter, and desocializes the aesthetics.
This saves code reviewers time and stress and helps them focus on what actually matters in the code.
And it only has to save more time than it takes to run "pipenv run black" to be measurably worth it.