I like it when people share information, “common knowledge” or not. There’s a lot of common knowledge I’m not up to speed on and I appreciate it when people share info on all topics. I think it’s good to lean more toward increasing the circulation of information than keeping things to ourselves just because they might be common knowledge. Edit: Also, even if somebody posts something that is common knowledge, it might spark a discussion that deepens everyone’s grasp of that knowledge or brings out some less commonly known information as the discussion continues.