Here is what Chuck Anderson says about formal study:

The Value of Formal Music Study

Should you study music with a teacher or should you "wing" it on your own? This question always comes up in this type of discussion about music.

An objective assessment of the two alternative approaches leads me invariably towards the formal route. Why? Because without guidance, there is a tendency to go in circles, What do you practice, when do you move to the next topic? When are you doing something wrong? How do you practice what doesn't exist to you?

Many complain about time as a factor leading to the decision not to study. I would suggest that exactly the opposite is true. Those with less time need the efficiency of study. Without it, there's a tendency to "practice" what you're already good at. Study ensures that you will be working on your weaknesses. The results of self teaching are obvious. A player may get good at one thing but have blatant weaknesses in another.

If you use famous players in the past as your justification for not studying, you'd be wrong! Wes Montgomery was self taught - there's your justification. But is it? Wes was self taught because there were no teachers at that time. I don't mean no qualified teachers. I mean no teachers. Wes told me "Make sure you study. Don't do what I did."

Chuck Anderson - www.ChuckAndersonGuitar.com