As a lover of books and exploring new topics, I too need to be mindful of my bookcases - making sure they are not overflowing and falling off my shelves. Books in feng shui relate to the life section of knowledge, which is wonderful, but having too many could create an in-balance of harmony.
courtesy of thissortaoldlife.com
Simply put, too many books in any given area of your home, let that be wealth, health, knowledge or career could relate to overwhelming the space (emotionally and mentally). It could feel weighed down energetically and visually, creating a it feeling of heaviness.
It's best to sort through your books from time to time and take an inventory of what you are really reading, will read and could be donated. By doing this, you create a constant path of movement that symbolically and literally allows for new knowledge and experiences to step into your life for expanded growth.