Re-reading a book is a lot like re-watching a film for me, I don't want to do it immediately, but there is value in doing it some years later where the details become less certain. I'm actively aware that even during tasks such as talking, my brain condenses and throws away most information. The import thing really is to develop and capture the right abstractions.

There are a few books I have gone back and read simply for enjoyment, for example Hitch Hiker's Guide to the galaxy was a pleasure to read. Some more dense materials that I know I will gain a lot from, I find it difficult to muster the motivation to re-read.

I read a lot of non-fiction, and while I'm definitely guilty (and proud of it!) of sentimentally holding onto old books, I think the value of having a personal library isn't to show off what you've read (an added bonus), but to be able to go back and reference books / passages when inspiration strikes or you realize your memory's gotten a bit fuzzy on a topic. Re-reading a book in its entirety is great. But sometimes just pulling back up a specific passage or chapter is all you need.

I reread and thoroughly enjoy "main sequence" John Irving novels every few years (at least Garp, Owen Meany and the criminally underrated Son of the Circus). I cannot recommend them enough.