I just reread the top-level faq. While it mentions the rep impact of community wiki, it offers no suggestion or advice as to when if ever a new user might be well-advised to check the 'community wiki' box on a question.
Then I read the community wiki official FAQ answer.
And the top-scoring, accepted, answer also offers no guidance as to when to check the box. It talks about 'posts,' but has nothing specific to say about questions versus answers. Further, the giant clutter of debate in the comments led me to abandon all hope of asking for clarification in this regard by posting a comment. So I'm posting this question to appeal to someone who feels up to it to enhance that answer.