Projection is crucial in live theatre.
To most people, projection refers to vocal projection, which is of course vital in its own right. But let us not forget the other type of projection; visual projection.
The definition of vocal projection I would hope would be obvious. By visual projection, I mean those non-verbal things which also must be projected into the "cheap seats" in order for a performance to be whole. A stance, a gesticulation, a type of walk across the stage, etc. All of these things, and more, constitute visual projection, and every actor on stage must make adequate use of such techniques in order to broadcast the emotions and thoughts of their characters to the entire house.
A person can be as loud and clear when speaking as the rooster at sunrise, but it will not be genuine if accompanied by physical stiffness and facial subtleties that cannot be detected by anyone sitting behind the first 3 rows. Honing in on better ways to visually project a performance is time well spent for the actor.To that end I sometimes watch and study the old silent films.
I would advise any actor to rent some of these seemingly ancient classics. Study the way the silent performers, (particularly Chaplin, Barrymore, and Pickford) conveyed, by necessity, impressive ranges of thought without the aid of speaking. With just the turn of a head and placement of the hands, watch people fall in love, become angry, be drunk, or prepare for attack. It is all there in the silent films, and nearly all of it is quite theatrical. (Not surprising given that most film stars of the day were live theatre transplants.)
As with anything, a balance must be struck. Silent movie stars, including the ones mentioned above, turned in many performances that by today's live theatre standards would be over the top and melodramatic. As often as not, the earliest films bordered on a sort of pantomime. Therefore, to stand and move on stage precisely as if one were starring in a silent film would be folly, not to mention totally false. Still, the world of silent movies is a gold mine filled with many example of flawless visual projection technique. A stage actor could do much worse than to emulate early 20th century cinema stars.
I encourage every actor to give at least one silent movie a try. They are still quite widely available in video stores. Plus, they are usually cheap to rent. You may be surprised at what you learn by watching the pre-talkie masterpieces of the motion picture world.