It's to do with giving more credibility to authors - so if you use different pen names, you might want to switch over to just one.
I think this could be useful for google to distinguish between posts of the multi-author blogs. Google search will try to display post by same author in the related search results, their this tag will be useful
I wouldn't do it on forums because a forum is a platform for discussion mainly (a forum post is roughly 50 words); on articles site, you write about your expertise (a topic is usually around 400+ words), do you see where i'm going with this?