You might be underestimating how helpful they are for the student. I would prefer seeing board work any day to a slide deck. Board work imposes a natural rate control, and seeing things cancel out makes mathematical concepts easier to internalize. Board work lets you see the sausage being made. Slide decks typically have the sausage on a platter with a neat little bow, I say typically. For me the best case scenario is that the instructor works thing out on the board, and has handouts of latex notes for students to take.