The guidelines (see this discussion) discouraging cross-posting duplicated questions seems to be limited in scope to multiple posts on SE sites only. In light of a recent post here, I realize that we haven't really had much discussion about how we should address cross-postings on websites outside the SE network. I'm curious to hear the thoughts of the community on this. Should we discourage it as well?
From a practical standpoint, I think that discouraging cross-posting on sites outside of the SE network does us little good. There's no mechanism for us to enforce it. I think of SE as its own ecosystem; if we import knowledge from outside of SE into the SE ecosystem, it's a good thing. For cross-posters posting outside of SE, all I ask is that if they get a good answer on the non-SE site, they should then post that answer under their own question (as community wiki, because it's probably not "their" answer; it should be properly attributed), so that everyone who visits SciComp can benefit.