The term "social circle" is a term people use to try to make themselves, and their friends, sound cool and important. The people you hangout with are either your friends, or they aren't. If they aren't, then they aren't a "social circle", a "flugelbinder", or any other gay term. They are just people you hangout with.
That concept hasn't changed since you were a kid in grade school. For some reason, when people become adults, they take really simple stuff that hasn't changed at all, and start using retarded terms to make it sound more important than it is.
Advocates of "social circle game" posit that it would make it easier to get laid because your friends may pressure or arrange a girl to be your girlfriend. Also you might get to be invited to parties, but for an average looking male he still needs to approach women who "show" interest in you in the form of IOI's. But this is no different from approaching a woman who "gives" you IOI's from school or work.