That means that you should code and document everything in a way that if you're run over by bus tomorrow, the project can still continue. In other words, you should make yourself easily replaceable by another programmer with a similar skill set to yours.
Being replacable, isn't that against the interest of a developer? In the book, 48 laws of power Rule 11 states that you should try to keep people dependent on you, in order to gain power, which then translates into monetary rewards.
Apart from the scenario, where you need some documentation for yourself in order to continue a project after 6 months of pause, there seems to be a clear conflict of interest here between the developer and the software company.
So as a programmer, should you really write excellent documentation and easily readable code for everyone; or should you write code and documentation in a way that it does the job and you yourself can understand it, but another person may have trouble understanding it?