“ Anything that's complicated (multiple interdependent templates, stylesheets, etc.) will probably be unwieldy.
More importantly, almost all content on Wikimedia projects is licensed under a Creative Commons BY licence, that is it requires attribution. If you cut & paste content you have to take particular care to provide such attribution for every single contributor of the original content. The easiest way to do that is to provide a link back to the original content in the edit summary so that the original's revision history serves as attribution. ”

“ The default is "Import to original namespace" which just copies things one to one: c:Template:Example → Template:Example. "Import to a namespace" will import the wiki page specified in the "Source page" field to the local namespace you choose, but will still overwrite templates etc. if you turn on "Include all templates and transcluded pages". Typically you'd use this to, for example, import: w:Wikipedia:Blocking policy → Wikisource:Blocking policy. ”

“ It fills up the revision history for the local template with every single edit on the remote project. This is bad enough when you mix local and remote edits, but it gets even worse when you import from multiple projects. Some of our templates now have several hundred apparent edits, that are a mix of edits made on Commons, on English Wikipedia, and local edits. It is impossible to disentangle them and understand the actual history of the code. In every normal circumstance you should leave this option unchecked. ”