Honestly the biggest advantage if you go for classes is you have someone to point out your mistakes and correct them. Many self taught guitarist often learn bad habits (eg. plucking with only one finger as opposed to using p, a, m, i fingering). And usually classes are structured in a way that follows your progress as you go along. If you're a self taught guitarist, you might make the mistake of attempting to learn a difficult song at the beginning. In the end, you might give up thinking guitar is difficult to learn.

I'm not saying self taught guitarists are no good but if they actually have someone to guide them, their progress will be much better