Community Wiki questions were once used for those questions that should not have been completely acceptable on an SE site, but would be of some interest for the community of that site. If you look at the questions marked CW (Community Wiki), you will notice that in most of the cases, they are questions were every answer is equally valid, such as in the case of a question asking a list; such questions are reported between the questions that should not been asked, in the FAQ.
To prevent your question from being flagged and possibly removed, avoid asking subjective questions where …
- every answer is equally valid: "What’s your favorite ______?"
Making a question CW was the only way to avoid that users posting answers which would be all equally valid (such as in poll questions) would gain reputation.
The other reason to make a question a wiki was to allow more users to edit the question; a normal question could have been edited from users with a reputation of at least 2000, while a CW post requires a reputation of at least 100, to be able to edit it.
Now users who don't have a reputation of 2000 can propose edits that will be approved from other users; making a question CW just to allow more users to edit it doesn't make anymore sense, nowadays.
You can also read what reported in The Future of Community Wiki, where Grace Note explains exactly what the future of CW posts is. In particular, see the following paragraphs:
Community wiki isn’t only abused for “fun” or “getting-to-know-you” stuff, though. Many sites propose using community wiki to allow content that is on-topic and useful, but can be considered borderline or questionable in other ways. Someone notes that a certain class of question has problems, and proposes using community wiki as a quick fix.
If a question is valuable enough that you believe it belongs on the site, chances are you don’t need it to be community wiki! We welcome all contributions which improve the quality of a site and advertise its greatness to the rest of the world. If you allow a certain class of questions, but only under the stipulation that no one can earn reputation from them, you’ve strongly discouraged these sorts of questions. People aren’t going to put in nearly as much effort to ask them.
Instead, strive for quality. If you’re unsure a certain question class belongs on the site, don’t tolerate the worst examples — demand that these questions be awesome. Questions shouldn’t be swept under the rug with community wiki; they should get the same respect and treatment as the rest of your Q&A. If those questions are something you are uncomfortable showing to visitors … they probably don’t belong on your site.
To notice that questions are automatically made CW when
- the questions are edited by 5 different users
- the number of answers is higher than a limit (I don't remember it exactly)
I have not found a way to search specifically for community wiki answers which makes them pretty inaccessible and hard to locate and expand upon to help future readers.
Search for wiki:1 is:question, and you will get a list of CW questions; if you are interested in CW answers, then search for wiki:1 is:answer; if you are interested in any CW post, search for wiki:1.