My DH still has his books from college, over 40 yrs ago, has never once used any of them as a reference for information. I have packed and lugged these things so many times.
I keep a diary of the books I have read with a mark to indicate worth re reading in the future or passed along. I give away more books than I keep. My post office has a trade shelf and then there is a community trade box that I use. I don't keep books unless they are really special to me. I always write a little note in the cover and sign my name and hope future readers will do the same as they are passed around.