One thing that I've found is that when using a big lens to photograph people, it helps greatly to act confidently and appear in a way that it seems like you belong there and know exactly what you're doing. When I photograph people on the street, I get all kinds of reactions from smile, a curious look, and also a "no apparent reaction". I ditch the shots where it seems the subject wouldn't have liked to be photographed and mostly keep those who take it with a sense of humor or are seemingly in their thoughts, or are interacting with others.
Small cameras and lenses are more inconspicuous, for sure. But confidence and a matter of fact approach (possibly a disarming smile) helps where a tense or nervous photographer might get an equally tense or frightened response from the subjects.
I find that practicing on the street gives me additional confidence to shoot documentary images at events.
