For me, it’s been fun to deface material that I personally found harmful at the time. Now, my relationship with selected books to be complicated. (More on this later.) To answer this specific question though there’s a sense of power in destruction and reducing a work to a select few words. It is a fun creative exercise that can be done either with preselecting words to show or going with a “gut feeling.” It keeps the mind sharp and is a different way to creatively express myself as a writer.