The first rule of old books is never throw them out. The day after discard is the day you will desperately need that book (which will be out of print and unavailable even in rare book stores). The second reason to keep old books is because they're like old friends. Once in awhile you run your hands across the backs of them and remember why you bought it and all the memories associated with it. Nah, don't junk them, If you absolutely must get rid of them give them away as presents. Disclaimer: I have book caches in three states.