I found lectures to be valuable only if I had reviewed the material beforehand. This was mainly because otherwise I just wouldn't be able to keep up in lecture.
If I had reviewed the material beforehand lectures were often extremely valuable for gaining new intuitions about a subject at hand that could be gleaned by an instructor's choice of explanation. And being able to ask questions in real-time was also quite valuable.
I wish I had realized this while I was still a student. By the time I was in grad school, it was too late. Now I make sure that I at least skim the material a bit before the lecture so I can see the other perspective, but also ask the professor/teacher any questions I had from my own pre-reading.
If I had reviewed the material beforehand lectures were often extremely valuable for gaining new intuitions about a subject at hand that could be gleaned by an instructor's choice of explanation. And being able to ask questions in real-time was also quite valuable.