This. I have family, military friends and recruiters and I don't want those conversations crossing over. With facebook, I have no idea what will leak across various groups of friends.
This isn't my use case, but a perfect example is people with kids. They're gonna share pictures and stuff of their kids, but as I'm sure you've seen, tons of people make comments like, "I wish I could just filter out pictures of babies and dogs!".
Even whatever you called it in livejournal where you had specific sharing groups of friends - that was a burden to maintain. I eventually lost track of my organization. It just wasn't worth it.
And it winds up being a better implementation of circles. The "circle" is object of interest. It's not a categorization that you put people in, it's an entity in its own right.
After messing up badly in the nymwars, forcibly joining together YouTube accounts with Gmail accounts they actually made a heavyweight but working solution:
It was given the name Pages which was more or less meaningless IMO (in this context).
What it felt like at the time however was a powerful solution for switching between pseudonyms connected to your account.
That said: Given a large reason for why Google+ is shutting down was that they had a couple of huge data leaks maybe we should all be glad kt wasn't too widely used :-]
That's the reason it's already planned shutdown was accelerated, but the leaks occurred after it was essentially abandoned to palliative care.
Had it been sufficiently used, and therefore actively maintained, they may not have occurred.
I really tried to be on team Google+ for a while but it was too little too late.