You can only learn so much on your own. You may have all the natural artistic talent in the world, but if you don't know how to market and promote yourself and apply it to career, you'll go nowhere fast. Though you will earn the title 'starving artist.'
Art schools provide a structured, educational-oriented approach to teaching the arts. You will learn to take a different approach to your art and learn how to apply your creative skills beyond the creative into the business/marketing side of the art world.
Being around other artists is also an invaluable part of growing as an artist. You will be subjected to artistic styles and approaches you might never experience. You will also begin to build your professional network that will become one of your best resources for your future career development.
Art School graduates go on to be fine artists, illustrators, animators, photographers, game designers, visual effects artists, art directors, producers and more.
There are more good art school options now than ever before. Art schools are located across the country in major metropolitan areas, and more recently online. Art schools like The Art Institutes, Academy of Art University, Full Sail, SCAD, are recognized as top art schools.
Check out Artstudy.org's art school directory that lists the top art schools. You can request info from any school of art that interests you.