Well, Google+ and many social networks feel designed to be opt-in so interaction between people that aren't directly connected somehow is limited and suboptimal. For example, some people I don't know have added me to a circle of theirs on google+ and have shared some bizarre pictures and things I don't care for, and I have to purposefully seek these out if I cared to look at them. That solves a lot of problems right there.
Some networks don't always work like that. It's the general idea of the thing more than it was google+'s implementation I was referring to by the end of that paragraph. I personally just want it in google+ out of habit, because I have it set that way in Facebook and all my dating site profiles and such. Inevitably I have a guy hitting on me and I don't want them to have a misunderstanding or to waste their time. It also helps to search for other people to talk to, and that benefits more than just me or my friends.
Some networks don't always work like that. It's the general idea of the thing more than it was google+'s implementation I was referring to by the end of that paragraph. I personally just want it in google+ out of habit, because I have it set that way in Facebook and all my dating site profiles and such. Inevitably I have a guy hitting on me and I don't want them to have a misunderstanding or to waste their time. It also helps to search for other people to talk to, and that benefits more than just me or my friends.