It is very common to criticize music instructors who emphasize exercises and scales for new students. Probably because many students are not patient enough to work through and acquire the skills needed to actually play stuff on their instrument.
While granting that often the right balance isn’t struck, the simple fact is new players are encouraged to do repetitive exercises and scales for at least two good reasons.
On the one hand we play the C Scale over and over in order to learn where the notes are and how they go together. That much is what we might call “theory”.
But on the other hand we play repetitive exercises to train our hands (and minds) to make the general kinds of moves we need to play the instrument smoothly and relatively effortlessly.
This is not theory. It is like a baseball pitcher learning to throw strikes, a soccer player learning to hit the top corner of the net, or a golfer hitting thousands of shots on the driving range.
It’s just that a musician playing scales is doing both things at the same time: learning a bit about theory, while gaining dexterity, strength and quickness.
OK. But What About More Explicit Theory?
The most obvious example of “more explicit theory” is learning how to read traditional notation. But there others such as learning about minor chords, different modes, odd and unusual rhythms, standard chord shapes, playing chords further up the neck, and having access to relatively unusual chords such as diminished, augmented, etc., etc.
Most of us can get by without a formal understanding of most of these things as long as we stay in our own little comfort zone or stick to playing with our regular band mates.
But as soon as we step outside of that comfort zone to play with other musicians – especially if they know more than we do, or approach things a bit differently – that’s when we find out how much we don’t know.
So it’s difficult to see how it would be bad to learn some theory. Probably the best way to find out which things you should focus on is to ask other musicians you respect.
One place to start might be an online forum moderated by people or instructors who share your specific interests. For example, if you’re into blues it would be hard to beat the advice you can get from Griff Hamlin.
The Guitar Professor has his own website where he provides practice tracks for aspiring musicians.