We sold or donated almost all the books in our collection about 14 years ago. They were taking up too much space, and I finally realized that in the unlikely event I wanted to read one again I could either get it from the library or buy another copy. I haven't converted to digital format yet, but probably will one of these days. Meanwhile I use the public library.
Quilting books, however - that's another story. I do re-visit the same books frequently, and my collection is always growing.