This emoji goes beyond simply taking a picture; it emphasizes that a special moment has been captured. It's often used when posting an outfit of the day (OOTD) or delicious food.

Back in the days of film cameras, the sound and light of a flash symbolized a 'decisive moment.' That's why it's also used to depict paparazzi photographing a celebrity or a press conference scene. It can even give off a "Got a scoop!" kind of feeling.