Because of my asthma and allergies it is a good idea to not have dust catchers on the book shelves. Some older books have mold and that's really bad for allergies. I find more and more, that I read on the internet. There are some very good authors sharing their work this way for free or a small fee. If you have a title of an older book you're interested in, go to google books and see if they have it online to read. If you visit publishing houses sometimes they have a free book to download. Oftentimes they have sample chapters to get you interested in buying new books. My daughter did this with her Kindle and ended up buying the author's whole series.
I donate my books to the local Senior Center, the hospital borrowing library, 2 nursing homes and my local freecycle group. Older textbooks go to recycle bin. Magazines in good condition, I leave at doctor's offices. Though pretty soon there will be no more magazines as I am not renewing them.
I don't make use of libraries because I'm terrible about returning books on time. I have never been able to break that habit and have spent too much paying fines. Not worth it for me.
Another rationale I give myself for clearing my bookshelves? I live in earthquake country. I have this queasy image of dying beneath an avalanche of books.
And still I struggle with the part of me that is kicking and screaming, holding on for dear life to every page as I self righteously pry them from her clutches.
First picture is one I took of my son with comic book character in Barnes and Noble, San Francisco
Second picture of books piled upon body is from: http://jalainer.blogspot.com