To do; Or not to do. Theatre.
Let me say the “quiet part” out loud. Most actors today want an excuse not to do theatre. They buy into anyone who tells them you don't really need to do theatre to do film and television. “They're two different types of acting.” “Theatre is too big for film and TV.” Two of the biggest lies ever perpetrated on actors. And many, many actors take comfort from those two heinous lies. Acting. Is acting. Period. Whatever the medium, your job is the same; Tell the truth under imaginary circumstances. And part of the best training in the business is doing theatre.
One huge reason, is that you are immediately rewarded for your work. With silence or laughter. With boos or applause. (Or more silence.) And it's an invaluable gauge of the truth of your performance. There is an essential connection with a live audience that any experienced actor engages and feels when they're doing film and television as well. Your crew is your audience. And, trust me, they're paying attention. They know. One of the best experiences you'll ever have as an actor is for someone in the film crew coming up to you on a break and saying, “You're gonna' make it. You're really good.” Almost every actor you admire has done theatre. I'll never forget being on the set of the cop show, “Simon and Simon” and all the actors got into a Shakespeare monologue contest including the leads. You wanna' be good? Get on stage.