I'll say upfront that I'm only describing my own experience here. What you do with it, and how you react to it, is entirely up to you.
As for the documents on my computer desktop — total chaos.
I save previous versions of manuscripts, people send me things, and I download draft layouts and edits — all of it in two languages. It all feels important somehow — what if someday I need to find the very first version of my book, or decide that some piece of text I deleted later was actually a masterpiece and want to use it somewhere?
Of course that won't happen — I'm almost certain... well, 99% certain. But I keep it all anyway, and my husband, glancing at my desktop from time to time, always grabs his head and tells me horror stories from the lives of IT people whose work computers are just as cluttered with old versions of programs, texts, and backups.
What to do about all this — I don't know. I suspect that, like with belongings we've learned to part with without looking too closely, I'll slowly start deleting things, freeing up megabytes of hard drive space for the next versions of the next books.
Maybe I shouldn't even be writing about this — maybe I should only write polished instructions: "How It's Done." But that's not really my style, pardon me. This is just who I am, and if anyone recognizes themselves in this, know that we're normal. We just hate wasting time. It doesn't get in the way of my working on books. I simply save a new version and give it a longer, clearer name: Book1final.definitely.v3.forsure.docx
Though, honestly, I probably should set aside a few minutes and just delete all the junk, or archive whatever I consider valuable. I'll delete it eventually anyway :)))