I like Bible Belt's and guru's answers here, they represent the two sides of this pretty well.
I tend to think that mass approaches are generally for inexperienced men. There is no shame to being bad with women, IMO. A guy who is bad with women will try to use mass approaches to help learn the social skills that he is lacking. Again, no shame in trying to self improve. Hopefully, the end goal here is that eventually, the guy will learn some social skills, he'll become what they call calibrated, and in the future he can approach a girl, but it won't even look like an approach. He can just casually chat with the women around him and have it seem completely natural and spontaneous (unless he's making a bold move as a point).
Like guru says, being able to approach is about being able to choose the women that you want to meet, instead of relying on luck or what women come to you. I wouldn't call that MASS approaching though, that's being selective. I still think mass approaching is more something that a newbie, or an inexperienced young guy might do. I don't think you should keep doing it for decades like Tyler from RSD, lol.
The thing I don't like about cold approaching as opposed to social circle is that you don't have any idea what the girl is like. She could be married, she could have a boyfriend, she could be an attention ho, she could be a prostitute, she could be a stripper, she could have an STD, she could have four kids, she could be psychotic, she could be scarred from being raped or molested, she might have a history of accusing men of attacking her, she could be $100,000 in debt, she could be a drug lord's girlfriend, anything. With social circle, you at least have some idea of what the girl is like in advance.