As soon as a photographer, amatuer, pro or otherwise, raises a camera at a human subject (or most wildlife come to think of it), the subject will change His,Her,(It's) behavioural pattern.
The conscious mind will take over from the subconscious and a behavioural presentation will be performed for the camera, introverted or extroverted acts.
Street shooting or Shooting from the hip attempts to capture the subject in subconscious behaviour.
Facial expressions will be authentic, as will the body language of the subject.
For the photographer and subsequent viewer it provides a stronger insight into the subjects character.
It is an art form that i am a long ways from accomplishing, In fact, at the time of writing, I have hardly experimented with this style at all.
Most of the art is to be inconspicuous, at nearly 2 metres tall I have alot to learn in this field. Most of my life I have needed to be the opposite, be seen, noticed.
Slipping under the radar and capturing someone from a metre away without them becoming aware is quite satisfying --- and fun, certainly moreso than photographing flowers!