There is no excuse to not have any documentation. One must always make an attempt to write a reasonable amount of documentation so there isn't a situation where there is no hope to understand anything except read all the source code.
But a lot of people (managerial types especially) expect docs will be "step 1 look here, step 2 look there, step 3 fix with this exact command"
Docs should explain how a system works, and perhaps some important places to look, but it's not a checklist to fix all problems. The consumer must still possess the ability, and will, to investigate and fix problems using their own critical thinking.