It really depends on the students. Stone cold beginners need a method book. Advanced students should be regularly evaluated and lesson plans made with a concept of progression and goal. I do work intermediate students through books like the Ross Bolton Funk Guitar book for a few months to work on 16th note subdivisions and basic mechanics though.I voted for "wing it", but most of my students are experienced, work hard, and are capable of self-directing their learning; I'm there to streamline, simplify, correct, clarify, etc.
I absolutely do use books for students who are directionless.
It really depends on the students. Stone cold beginners need a method book. Advanced students should be regularly evaluated and lesson plans made with a concept of progression and goal. I do work intermediate students through books like the Ross Bolton Funk Guitar book for a few months to work on 16th note subdivisions and basic mechanics though.