As I am recently retired, I read more now than I ever have since my school years. I found it curious that people might make marks in a book for any reason. I prefer to keep the book original so that the next person doesn't have to interpret what I was trying to glean from the text.
Ahhh, the world consists of two types of people: those who dog-ear and annotate their books and those who keep them pristine. I belong to the first sub-population, you to the second :))
Most books I buy are hard-cover. When I'm gone, I pray that my family will give them to the local library. That is why I don't want them to be defaced in any way. It's not about me.