Depending on the context of the community, such things can actually do more harm than good - many users react negatively to any display of authority, no matter how reasonable it is. I don't think community managers should have to subject themselves to the questioning of users who don't have anything better to do, if they don't feel like it adds to their community.

Of course, this does work in some places - Wikipedia is extremely transparent about its moderation actions and policies - but I don't think it should be the default for every single community.