Will documentation be the death of me? Was it for you?

I run a small design agency. When I hand off a brand or website package, I include lightweight documentation, and honestly, if the client never opens it again, it's really not that big of a deal. Sure, their brand might look inconsistent, or they might break a module on their website, but then they come back to me to fix it, so yippee!

Now I'm building a SaaS product on the side and it's dawning on me that this is a completely different problem. You ship new features, the codebase starts to balloon, and hopefully, someday, there will be a team who needs a single source of truth to reference. Suddenly it's a very big deal if what's written in your docs stops matching reality.

So for those of you further down that road: when did an up to date knowledge base stop being a nice-to-have and start being a necessity, either for yourself or your customers? Was there an "oh shit" moment — a bad onboarding, someone building on an outdated assumption — or did it just gradually get worse until you were forced to do something about it?