Bill the Lizard said that
CW really isn't used anymore since anyone can propose an edit now
What are Community Wiki answers now for?
Related: What are "Community Wiki" posts?
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The intent of community wiki in answers is to help share the burden of solving a question. An incomplete “seed” answer is a stepping stone to a complete solution with help from others; an incomplete question is a hindrance and an obstacle to getting a solution as no one understands the inquiry. It is in answers that the goal of community wiki, for the community, by the community, shows its truest colors.
If you know that your answer is incomplete and you want to encourage other users to add information to it, you can make it CW to invite others to edit the answer. Since everyone can propose edits, community wiki is not necessary anymore for collaborative answers, so it has lost a lot of its usefulness. It is now more of an invitation for other users to edit, but it is not really a technical necessity anymore.
It is rather used as a sign for others that you don't mind, and even encourage other users to edit the post. Many users hesitate to make big changes to posts belonging to other users, CW means you relinquish the sole ownership of the answer and encourage other users to add to the answer.
I've posted this a few other places (originally on the Music Meta) but since you want more answers I'll paste it here. Note it completely agrees with Fabian's answer and the blog post, though it predates them :P
Community Wiki is:
Community Wiki is not:
As above, Community Wiki is useful when information it constantly being added and updated. This is why posts are automatically made CW after 10 edits or after being edited by 5 users. Posts should be manually marked CW when intention is to have this collaborative editing. This is normally done to questions, to ensure all of its answers will be CW.
Community Wiki posts stop giving reputation (due to upvotes) to the original poster once they are made CW. When you have 90% of the content from a post coming from other community members, for example, why would you want rep going to only one of them? CW neatly solves this problem.
This is why CW is bad for opinions, recommendations, and list questions. If someone provides a useful opinion on something, they should get reputation points if others find it useful! Those do not need to be collaboratively edited, and neither do lists; a new poster will just add a new list item as a separate answer.
What are "Community Wiki" posts? (Meta Stack Overflow)
This post is a good example because the nature, purpose, and application of Community Wiki has been repeatedly revised. As such, the answers have needed to be revised over time, regardless of whether the original asker and answerers are around to update their old posts. The appropriate knowledge should be added by whoever has it at the time.
How do I root my device? (Android Enthusiasts)
This post is a good example because new Android phones and tablets come out all the time, in addition to software updates. The methods for rooting are not the same between devices and software, and so they are constantly revised. Anyone who reads about a new rooting method or tool can post it in the answer. This also is an incredibly useful resource because it eliminates the need for hundreds of "How do I root Device X with Android version Y?" questions; instead, we can gather it all into one cohesive wiki.