There comes a time when every book starts to fall apart and it just isn’t worth trying to save. There’s many other copies in better condition and there’s nothing about THAT specific copy that merits repairing a broken binding or putting up with missing pages. Such old, tattered books are the perfect material for altered books. Altered books are simply books remade into new and interesting artwork. They’re no longer readable as a standard book, but are given new life as art.
I occasionally have customers come in looking for just this sort of damaged book. The book is interesting looking on the outside, has interesting old illustrations, etc. but is in poor shape overall and really has no value as a book anymore. I like to think when they haul away those damaged old tomes they’re off to be turned into beautiful things, like a butterfly emerging from a chrysalis. Looking at that ugly old thing you’d never guess that there was life left in it, let alone something beautiful.