It suggests that this is not the ideal sort of question for the site, and that any future attempts at similar questions may be met with greater resistance.
Additionally, if the relevant information ever changes, no new answers can be submitted.
I posted an answer to a question that had an accepted answer, and it gets upvotes once in a while. The accepted answer was correct at the time. My search for the answer later turned up the SO question and answer plus the new correct answer from the cmake site. So I posted my new information as a new answer.
I think if a question is closed, that would mean no corrections or updates would be possible.
There is a lot of linking to other SO answers, so if someone asks a question about new information, you can still refer to closed questions and expound on them.
I'm not sure if that's the best way to do it, but it's an option.
Additionally, if the relevant information ever changes, no new answers can be submitted.