As you can probably see for yourself, Musing at it's core is just a simple question and answer platform. But that's just an overly simplified statement. You see a question asked doesn't only help the questioner but also helps other members of the community who may have the same question. Then, there are answers on those questions, the most fascinating part. Every one pitches in his own opinion and everyone's opinion matters here and is valued properly. So, that's what musing is.
As, to why did I join? Well, the answer is obvious: value to the content and support of the community in terms of knowledge sharing.