If you make yourself disposable you are far far more likely to be disposed of then promoted in 9 out of 10 companies.
I would even go as far and as cynical to say that if the documentation you create is so good you will just be replaced with by cheaper staff, outsourced or freelancers/contractors.
edit: honestly, the worst advice i have ever read on HN in like 10 years. you relationship with your employer is based on leverage, if you make yourself too disposable you are skewing the balance of power against yourself.
fwiw i am always a happy to provide basic docs and support to team members but i'm not going to document or automate myself out of a job. i've seen it happen too many times.