Don't go looking for Google+ History. Right now, it's available only to developers so they can support it with their software. Google will make it available to users later.
In a nutshell, Google+ History will make it possible for third-party apps, sites and services to share information about your online activities with Google+. For example, if you post on Twitter, a copy of your tweet will show up in your Google+ profile.
Google+ History doesn't actually share content from the other sites with your friends. Instead, it places it in a secure, private space on Google+ where you -- and only you -- can see it.
If you would like to share any of these items, you have to explicitly take action to do so.
In my opinion, this is how social sharing should work.
Using Google+ History
Details about Google+ History are hard to come by. But it's pretty clear what Google hopes to accomplish.
Right now, Google+ History exists only in the form of an API, a programming interface that enables software components to interact and connect, and as a preview for developers for testing their software.
Google+ History is functionally similar to Google's Instant Upload feature, which automatically uploads pictures you take with your phone to your Google+ profile without sharing them with anyone but you.
When you create a post, you may choose to include any of the phone pictures that have been uploaded via Instant Upload. Or you can ignore them.
In fact, it's helpful to think about Google+ History as an expansion of Instant Uploads -- it expands the types of content that can be "instantly uploaded" and makes "instant upload" functionality available to companies beyond Google.
The magic feature of both Instant Uploads and Google+ History is the instant and automatic uploading of content that is not shared until the user deliberately shares it.
In other words, it doesn't share content for you -- it locks and loads it for you. The content gets shared only if you take action to share it.
Here's how I think users will experience Google+ history.
As third-party websites, online services and mobile apps increasingly support Google+ History, they'll add Google+ to the list of options for sharing what happens on their services. If you agree and choose to authenticate Google+, everything -- or some things -- you do on that service will show up on your Google+ profile, but only where you can see it and nobody else can.
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