For actual study of any topic it is important. It gives insight into how the person thinks. They become a literary treasure for famous writers papers when they pass on, like Lorraine Hansberry for example. A basic function of a real book is to have a margin which intellectuals for years had used to mark up, write notes to themselves. Serious people using books for serious purposes not only highlight, but also notate.
I thought it would be great to have the ability to notate without clunky on-screen keyboards a book. The answers on this page have helped me decide to not buy an iPad pro.