IF you want to work as a corporate artist, then YES, you must go to art school, just so you can show your diploma. It's not needed for any other purpose. It's just a hiring requirement.
IF you don't know how to do something (e.g. draw), and you need guidance, then YES, you should go to the art school (or become an apprentice along someone else that can provide some certification).
IF you are after to become a 3D artist, then YES, you must go to school, both for diploma, learning reasons, and getting connections with hiring companies.
BUT, for any other combination (e.g. freelance artist) who already has developed their skills on their own, then art school is the biggest waste of money & time thing they can do in their life. Art school in this case, will not give them anything that they need. It will instead be a 2 year waste of time, and a lifetime of debt.
If you have already developed your style on your own, all you need is to learn how to do business, so you can sell your art as a freelancer. And that's something that art schools don't do. They're absolutely useless in that department.