I am of the generation that was taught diagramming as a matter of course. I have used it, and I think it is helpful because there are so many students who have not a clue about sentence structure. It's interesting to me that there is, as there should be, so much emphasis on hands-on learning and on graphic representations, but diagramming, which combines both so beautifully, has been largely neglected.
Stanley Fish has a book, How to Write a Sentence, that focuses on shape and structure in a way that I found very helpful in teaching, too. In some ways, his book is almost a "diagramming plus" endeavor. He divides sentences into a few different forms and takes off from there. There are no doubt those who find all of this formulaic, which it is, but students who don't know the formula have nothing to build on.