I haven't done anything with them so far. I mean other than reading. There are some books that I have re-read. For example Szakács Eszter - A Szelek Tornya and Szakács Eszter - Babilon. I like those (Hungarian) books very much. Especially the Babilon.
I also have complete book series. For example Jess E. Owen - The Summer King Chronicles. There are currently 5 books in that series. Or Michael Peinkofer - Gryphony. There are currently 4 books in that series.
But once I have read a (novel) book in general, there is no practical use to keep that book, because I know its story (this is also true in the case of the above mentioned books). Except (for the practical use), if you are a book collector. But I am not a book collector. However, I still have (all of) those books. They are sitting on the bookshelf. Maybe I will sell them later.
If no one else wants it I'll burn it off
when we have a book that we have read it means that it is old and stored properly.
the thing that we have to do is to keep the book in a good place and suitable to be stored or not exposed to rain or do not keep it heated up because it can have a negative impact on the book.
and old books that we have read even many times, we must save the book, because in the book it contains a lot of knowledge if it is openly related to education, so keep the old book well.
because the book can always be used if the book is still good and good.
then the thing I did with the old book I had read was by storing it well and good so that other people or our descendants could read it like our children or relatives.