I have a smallish two shelf bookshelf mostly full of books for work. I bought the latest of the books at least ten years ago, and the others in the years between 2002 and the year I bought the final book.
I don’t remember the last time I consulted one of those books and that bookshelf would come in handy for other books I actually read.
Maybe during the next book purge I will get rid of some of these.
Cedar Waxwing's 365 
I’m guessing they’re the sort of books that get updated often, but they still might be worth something. Easy enough to find out. I’ve sold hundreds of my husband’s chemical engineering and other science books on eBay and Amazon, and a few of my son’s IT books.
I don’t think they are worth much, but when the time comes I will check it out.
I need to confront my work books.
Any work books over 10 years old, unless you are a history professor, need to go.
I agree for the most part, but some books on my shelf are still relevant. The basic principles of Web accessibility haven’t changed, only the guidelines.
I have a shelf like this too. Sigh. I would love the money back that I spent on them.