"In a lot of ways a Community resembles a Google+ Brand page, except it can be open for posting by numerous members, not just the moderators. One interesting feature of Communities is that you can share into them from the web using the +1 button. ... if you belong to the foodies Community and find a fun recipe on a random website, you can hit the +1 button and then chose to share with just that Community. "

The latter could be good for people like me that just like to stab at buttons to share stuff they see that might interest a group.
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