There's a widely known issue with social networks—they're impossible to keep up with. Something is always happening, and unless you follow only a handful of people, there's no way you can read all the content that streams by.
To get around this, some networks have taken their own approach to resurfacing content you may have missed. Facebook and Twitter do this. Now Google+ does as well.
Today users are noticing that when they go to check their Google+ notifications, an entry at the top shows how many posts they've missed from people they show interest in. Tapping this pulls up the presumably fascinating content.
So far these notifications appear regardless of if you haven't used the app in weeks or if you just swiped through a few hours ago.
Like YouTube's new video suggestions, this change is intended to keep you using Google+. Online services don't like when you leave. Besides, doing something else causes you to miss stuff... and then getting a notification about it.
Alternate title: I Don't Actually Care But I Know Some Guys Who Were Really Pissed Off By This One Google+ Tweak