It has to do with who the person who’s skin was used as a book binding was. We have no idea. This would be no different from archaeologists today doing facial reconstructions of a skeleton in, for example, an excavation of a medieval Christian cemetery. Any information about the past could be important. Especially when it comes to humans. It’s preserving it for the sake of basic scientific investigation into the person so that we can learn as much as there will ever be possible to learn about them.