You’re just logged into some bullshit while browsing the Internet. This next part, however: “… and gives Google that common understanding of who you are.” Now we’re chewing on something a bit meatier—as in, an admission from Google Inc. that Plus mostly exists to gives the company a better “understanding” of you.
The G+ network is merely an excuse to gather more data about you. No utility whatsoever. We. Are. Ads.