Of course there is no upside for spending time updating documentation unless it actually is part of your job description or there is legal requirement for company.

If you put knowledge in wiki, no one will read it and they will keep asking about stuff anyway.

Then if you put it there and keep it up to date you open yourself to a bunch of attacks from unhappy coworkers who might use it as a weapon nagging that you did not do good job or find some gaps they can nag about.