If you're thinking a question should be CW because it can't garner useful, objective answers... Then you should probably just vote to close it. From the FAQ:
If your motivation for asking the question is “I would like to participate in a discussion about
______”, then you should not be asking here. However, if your motivation is “I would like others to explain
______ to me”, then you are probably OK.
(and also the guidelines for asking subjective questions, linked to from the FAQ)
If it's actual, useful stuff, then CW isn't necessary:
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.
Why would you need Community Wiki on a question? Well...
Sometimes you have content which is valuable and on-topic, but is perhaps a bit too popular. It runs the risk of overwhelming the rest of your site if it grows untamed. In these circumstances, community wiki can be a way to preserve the value of these posts while stifling their growth. Keep in mind, though, that in using community wiki to stifle growth, you should actually follow through with it — a site should never have more than one community wiki question for every hundred questions. Having too many community wiki questions defeats the entire purpose.
So again, first ask yourself if the question even belongs on the site. Then ask if it could be structured so as to encourage high-quality responses. Finally, if the question belongs, encourages and is receiving good answers, ask yourself if there's a really good reason why the site should encourage editing existing answers over posting new ones - that would be when you might ask for it to be made Community Wiki.