Wikis on Wikia are founded with the intent to not only build vast databases of knowledge, but help unite fans into a sense of community. As these wikis evolve and expand, the temptation to create similar or duplicate wikis grows. While users are very much able to copy most content under the CC-BY-SA license granted proper attribution is given, the question becomes whether or not one should actually do so.
When to copy content?
One of the best times to use content copied from another wiki is to help enhance areas of the wiki which are not the primary focus of that wiki. For example, a wiki dedicated to a film may recognize they are not experts about the background of the actors who portrayed the characters. Adding content created by a more specialized wiki may be the better option than spending additional energy on an article that is of lesser importance to the wiki's goal.
Some communities are more fractured than others, commonly the result of user disputes or policy disagreements. In these cases considering to copy content for a new wiki should generally be a last resort. As a member of the community, your voice matters. If the dispute is with an Admin, consider talking to them about their actions calmly or with the community about whether or not they should continue in such a position if they are unruly. On most wikis policy is created by the community so voice your opinions in the wiki's forum or policy talk pages if you disagree with a specific aspect of the wiki's rules.
When not to copy content?
Copying content to create a duplicate wiki is in no one's best interests and in some cases can get the wiki closed down (such as duplicating the favicon, wordmark, or background). Avoid creating a wiki on a subject that already exists without first trying to become a member of the original community.
A diverse and united community is the driving force to great content. Content is often created by more than one user in hopes of constructively bettering the wiki they edited. While licensing allows for their edits to be reused, copying edits goes against the intent of those edits. Doing so can easily create hard feelings and divisions between fans: readers and editors alike. Instead of fracturing a userbase, consider consolidating energy into building the go-to-site for the fanbase.
Alternatives to copying content should be considered whenever possible as unique content is better for a wiki's SEO anyway. The creation of derivatives, new articles based on existing articles, is a far better choice over straight copy-and-paste, however, don't forget derivatives of copied content must be properly attributed as well.