Maybe you are a reader, and like me, you still enjoy the physical copy of a book. But unless you have a big house with a library, keeping all the books you ever read and enjoyed is not a possibility. I love books, I love to read. I grew up without a television, and reading was the main distraction, especially during summer vacations. I was fortunate that my parents had a big house with an extended library. There was no computer or internet at the time, so we had more time to read.
But for the majority of us, our bookshelves have a very limited space, and when your books start piling up on top of each other or in some corners of your home, it is time to start sorting the ones that are very specials and worth keeping, from the ones that you didn't really enjoy and would not recommend. It is also a good time to check the books that you still need to read and forgot you had.
I did just that, and found some great read that had been given to me and some not so great read that I knew I would never read. I took my time (I enjoyed it) and checked each book with goodreads.com, read the summaries, some of the reviews. As a result, I rediscovered a few books I wanted to read and I saved a lot of money on books I didn't need to purchase for my summer reading.
So what book do you keep? Well, ask yourself the questions: why do you want to keep it? Is it a book you feel you'll enjoy reading again? Do you want to be able to share it with someone else? Maybe it is a reference book or some part of it are so great that you want to be able to get back to it? Or is it just for decorating purposes?
It you're keeping a book so that you'll remember you've read it, don't. You can keep a book log, make a summary or a review, rate your book and give it to someone else. That's one of the reason I enjoy goodreads.com. I can share with some of my friends some of the great books I read.