During my final week when I was doing code handover I sent an email around the company pointing out that the wiki would answer most of the questions they might have about the apps I worked on.
Three months later my phone starts ringing. I was in a new job so I didn't answer, but they kept ringing. Then they started calling my wife as she was listed as my next of kin. My wife also didn't answer as she was with a client. After a few hours, my wife picks up the call and texts me that my previous employer was desperate to speak to me. So I called them during break and after a bit of an ear bashing I was informed their whole warehouse system was down and all business had stopped.
After a bit of diagnosis I realised that they had fallen for the first gotcha I listed in my docs, they deployed the wrong DB driver. I asked why they didn't read the docs. They responded "what docs?". I explained that I sent an email round before I left with guidance on the app. Rather than apologise they berated me for not doing more to alert people to the existence of the information. It was that attitude that contributed to me wanting to leave the company in the first place.
I think the moral is that no matter how good your docs, some people will always ignore them even when the world is collapsing around them.