Excess books

I tend to read my books over and over again. Not right away mind you, but I save them for reference (if they lend themselves to that process) or for their exciting nature, etc or even a couple for nostalgia. But I run out of space no matter what I try and do. (I have given away about 20 in the last month)

Do you reread your material or read and toss, or read and save for eternity for God knows what reason?