Why sort everybody into just one circle? Most of my contacts are sorted into multiple circles so that I have more fine-grained sharing control. G+ also makes it

Why sort everybody into just one circle? Most of my contacts are sorted into multiple circles so that I have more fine-grained sharing control. G+ also makes it fairly easy to create new circles on the fly for when I want to share a message with an even more specific group. I think of Circles more like tags that I can use to control visibility of my posts.