As part of my site assessment I decided to actually type up the books in my home library that are permaculture-relevant. I noticed several things.
First, I have many cookbooks (mostly vegetarian) and many field guides, but fewer gardening/plant care books, and almost no books about home repair, building, permaculture design, etc. No books at all about water management, though I do have some on my wish list.
I have one book on health - a tea tree oil book - and that made me realize it would be good to have more health reference, both allopathic and naturopathic, in the house. While it is true that those books can go obsolete quicker, if the internet was out it would be great to have a way to look things up, especially if I had a sick kid.
I also noticed that several of the cookbooks are ones that I'm not sure that I ever use. It might be worth replacing them with other books that I find more appealing or helpful. I could always get an encyclopedic book like a Fannie Farmer Boston Cooking School if I want a reference.
One of my books was a surprise - It was a hand-me-down from a friend who left the country and I had always thought it was a building book focused on new construction as she gave me several like that but it's actually a much more useful home repair book.
I have 2 books that I classified as problematic, and I have to decide what to do with them. One I may just give away, possibly with a note on the cover, and replace it with a better option in that category. I may keep the other one - it's fairly old so a lot of the contents are obsolete, but it's a charming read and it does have some practical content that's still usable, like how a smaller person can safely do heavier tasks.
Edit: I did donate that book, with a warning note on the cover. I also went to the library and browsed with my home library in mind; I'm going to read some more books and consider them for my wishlist, particularly an herbal encyclopedia that I checked out.