I didn't go to an art school, but I'm also not a professional artist by any stretch of the imagination. My focus in education has been software development, and art a hobby, but a number of my friends from back when I took art in high school split off to various art schools.
Generally, with a career in the arts, your portfolio speaks louder than your degree. The purpose of art school isn't to come out at the end with a certificate though, it's to guide you through learning and improving your art, with the mentoring of skilled professionals and tutorials to teach you new techniques.
On the flip side, if you prefer self-teaching through resources (art books, online tutorials, etc.) then you would do better to not take the classroom approach. You can instead apply all your time to the skills you want and the way you want to use them, and in doing so save some money that you would otherwise spend on tuition.
I personally do better in a classroom scenario. I would have liked to take visual arts as a minor in university, but it wasn't an option (apparently you can only major in it at my school), but back in high school I absolutely loved my art classes and felt I improved in them far more than I ever have with just online resources and practice on my own. I do very well in a public environment, peers for constant critiques, and a teacher/professor to explain and show concepts tailored specifically to whatever I'm working on.
I'll probably go back to taking art lessons once I'm finished university, just at a community center in Toronto or something, but I have friends who hate their art schools and much prefer self-studying. @marc advocates against attending an art school, if I recall correctly.