My mom is a music teacher, and she finds that she often will get new students who were previously self-taught with blind spots. Ideally, one of the main perks of school, which is difficult if not impossible to get with auto-didacticism, is that you get continuous feedback from someone who knows what common mistakes look like.

My technical background is largely from reading books and manuals on my own, but I'm under no delusion that I would benefit greatly from some more formal instruction for certain topics, if nothing else because then I would have someone challenge me immediately when I'm wrong.