According to an article on Search Engine Journal,
It will be interesting to see if Google+ Communities catches on in the same way that Facebook groups have done. Unlike with Facebook where users need to navigate to a particular group before posting something, it’s possible to post an item on Google+ Communities directly from the Google+ home screen. Simply post whatever it is you want to share, and then select the appropriate community circle to make it appear on the relevant page.
However, Google+ Communities do have a few key differences from Facebook's Groups. Some of the new features include the option to filter posts within a community by category or topic, larger photos, and hangout/event sharing directly on the Community page.
The implications of these Google+ Communities are exciting for SEOs and businesses. It will be interesting to see what people do with the new feature to boost their brands.