The thing about any kind of cold approaching that bugs me, whether it be day game, night game, clubs, whatever, is that you never know who you are approaching. She could be a single mother of six, she could be a hardcore BPD b!tch, she could be married, she could be diehard lesbian, she could be the cheating wife of an mafia boss, anything. Online profiles are full of lies.
So the nice thing about social circle is that you have a pretty good idea of who you are hooking up with, and whether or not there might be some attraction. The downside is that if you have a small social circle, there may not be much variety there. When you think of social circle as "everyone you know" though, it's probably a lot bigger than you might think. That's admittedly not a very "PUA" way of looking at things, though.