We Librarians cull a lot these days. Fiction and Nonfiction books have a shorter shelf life. I often compare our policies with that of a supermarket; if the book (product) has not been used for a specific amount of time you can consider there is no longer any 'customer demand' for the title and the space it occupies can be more 'profitably' utilised. You are better to replace the book with titles that are worth their place on the shelf.
Having withdrawn thousands of books (and yes sometimes with pain in my heart but more often with a smile) I've had lots of thoughts what to do with them. Our maintenance team and I created little tables of encyclopedias and I had ideas to use some of the books as actual book shelves but that never happened.
Here is a great idea for what to do with old books that you might not want to throw out but that is of no use to the library anymore; make a Christmas Tree out of it.
This Youtube video shows you exactly how to do it: https://www.youtube.com/watch?v=sKvPJljPiYQ
Very simple and you can embellish the tree or transform it into an angel if you put a little Styrofoam ball on the pointy top and cut wings from another couple of pages as you can see on this Youtube video: https://www.youtube.com/watch?v=X_DXjR8xlH4
You could make several and hang the angels from an upturned umbrella frame, as if they're flying…..
What a great way to see something that is no longer used being transformed into something beautiful!