I will keep the 1st editions, and most reference books.
I feel can toss everyone of my computer books. (Not one did I find well written, or worth keeping. If anyone decided to write a computer/programming book take out every unneeded word. Maybe take a technical writing course if you live near a good university?)
It's just hard to get rid of reference books.
He's died now, I took over the flat, and moved from a family home into the same flat. I also had to shed a lot of books in the process. I ripped my large CD collection to a media server. I miss some of those books I got rid of; but I like this small flat, and I don't want to dedicate a small room to a library.
The first books I got rid of were computer books. They were all manuals for some obsolescent technology; like, I thought the "Rhino" Javascript book would be useful forever (um, no). I got rid of a few feet of books on Buddhism, and several more feet were books on Western philosophy from my undergraduate days. These were books that had been formative for me, but I was honestly never going to open them again.
So I don't really agree with my father's advice. If you regret ditching a book, you can just replace it.
That's what the internet + ebooks are for.
Unless a book has a special meaning to me personally or is considered life changing, I rarely keep any physical books.
With technical books, I often need to jump to another section, which is so much slower and more painful than with dead trees. Code formatting also tends to be abysmal on my reader—although books are not the best for this either. Maybe I’m not using my device to the fullest?