It is a technique employed to command respect and attention, such as when a teacher talks to a class, or simply to be heard clearly, as used by an actor in a theatre or during drill.
The goal is to isolate and relax the muscles controlling the vocal folds, so that they are unimpaired by tension.
Actors are taught to stand erect with the feet shoulder width apart and the upstage foot (foot farther from the audience, when not facing the audience) slightly forward.
In singing, voice projection is often equated with acoustic resonance, the concentrated pressure through which one produces a focused sound.
The size, shape, and hardness of the resonators all factor into the production of these overtones and ultimately determine the projective capacities of the voice.