I'm self-taught on the majority of instruments I play (except when I had violin and drum lessons), but I guess I'm pretty lucky because I was taught music theory and had performance lessons throughout high school. I found having an instrument tutor slightly restrictive - since they'd choose what you had to learn, even if you hated the song (I always like playing something I actually want to, because it motivates me to really learn it). I also didn't have that much luck with 'good' music teachers. I'd have my tutors discouraging me or put down the way I was playing without being helpful, so I'd end up browsing the internet/reading books to help me learn instead.
The benefit of having the music teacher was learning all the techniques, terminology, correct positioning, and also, how to pull apart a song and fixing your mistakes. E.g. rather than playing a song a million times over, play the song once - take note of which parts were difficult to play/where you made mistakes, and go over them. Figure out why you made the mistake, and try to fix it. You could do this by maybe playing that part a different way - playing it at a slower rate, or mixing around the rhythm. It all depends on how you learn best though. I know a lot of musicians who have been self-taught all their life and are brilliant at what they do now.
/End of life story.