I don't know how many books I've accumulated over the years, probably hundreds. Eventually I have to go through them and pare down my library. This will be a continuous process. Below is linked the Awful Library Books blog and a PDF of a weeding manual. Taste is subjective so one's "awful" books are another's "wonderful" ones, and vice versa. Librarians try to make the weeding process as objective as possible, e.g., books that haven't been checked out in several years.
CREW Method (weeding manual).