Edited: Google announced the new Communities feature exactly one year ago, on the 6th DEC 2012.
We have come a long way since then and it just gets better.
New Community features are expected, our Feedback has been heard.
What is the difference between a Google+ business Page and a Community?
For solely marketing purposes a Google+ business Page can be used to let people know about your campaigns or for reporting on business topics: A Community needs more presence and interaction but also begets much more engagement to the owner.
I hope you don't make the mistake of total content automatization: Just dropping links or Twitter style posts with Hootsuite or similar is not a good practice. The scheduling tools are a great help but you still need well crafted posts and good content. Leaving questions or comments unanswered especially on your own posts just shows, that you don't care about your potential clientele. Tsk tsk.
Creating a community gets you closer to the users and possible leads:
Be present, engage, produce / reshare interesting posts (not just ads!) and try to make the members of your community feel welcome.
Take good care of moderating the community, cleaning spam and moving posts to correct categories.
With my Google+ Helper Community I'm aiming at creating a Google+ information library: The search works well, one can browse by topics and if the moderators know what they're doing, the question posts are in the right place - with spam nowhere to be seen.
One can also share links to any community category, using a link shortener is perhaps recommended: Here is the Tips & Tricks category from the official Google+ Help Community:
I like the way +martin shervington has put it:
Communities are an incredible feature from Google Plus. Since their launch, there are around 50,000 listed communities on Google+, some with tens of thousands of members, others with much fewer. No matter whether you are into photography, business, education, fashion, or just about anything… There could well be communities already available for you to join, or you can make them yourself… It is a little like forming or joining a tribe!
Only the Google+ users can join communities -> comment and share / create content. But anyone outside Google+ can see the posts in a Public community.
It's not so much a question of just showing what you sell, but engaging and interacting with those who are interested in the product.
Learn more about using communities
+Debi Davis created a minute schedule for the Hangout on Air video about Getting the most out of your Google+ Communities, which makes it really easy to check upon different points in discussion:
Create your own private community
You can use the same idea for corporate communities, project communities or classroom communities. 20 categories and 10 link places in each community.
"At most organizations, it's important to make sure that private conversations remain private. Google+ is an ideal tool for groups who want to have social conversations--without broadcasting their thoughts to the world. There's an extra layer of security in restricted communities that only users in your organization can join.
Whether it’s designs of your beta product or notes from your team off-site, anything you post will remain restricted to the organization."
Videos about Google+ Communities
Learn more about Communities - Google+
Top 20 communities your business should join
Join a Google+ Community - Google+ Help Center
Most popular Google+ Communities by +CircleCount
User Guide for Google+ Communities - +martin shervington
Real Communities Require These 4 Underlining Factors - +David Spinks
Why Communities matter on Google+
Create a community for School or Work - Google Apps
Sharing restriction for Apps users - Google Apps Admins
Anything else you'd like to know about the Google+ Communities?