Your job as a screenwriter is to create a movie in the mind of your readers. You must draw us into your story by providing a clear picture of what we’ll see on the screen when we watch your film. You can’t do that without description! Heading a scene EXT. CHICAGO or INT. APARTMENT and then jumping right into dialogue creates no image at all, and is more of a felony than a misdemeanor. It will definitely kill your chances for a deal. Even action alone doesn’t do the job. “She answers the door,” or, “She pokes out his eye,” may create a picture, but it’s so vague and indistinct that the reader will become bored or frustrated. Even if you’re a novelist — I should say especially if you’re a novelist — you must employ succinct, vivid description along with your narration, action and dialogue. We want to imagine your characters, inhabit your settings and be transported into the world you’ve created. So describe it!