They need to hear what the scene is about because part of the fun for them is the journey to that result. I think the actors trust talking to me because I'm able to speak in a kind of language that is more acceptable to them. On the downside, the actor in him creeps to the forefront more than he'd like. When the actual actor's take is different, it sometimes takes me a moment to divorce myself from the original performance I had in my brain. Since actors are the ones performing, writers must be able to let go of the words they've written, which is often not a simple task.
Writers are a little more rigid.
In that way, there's an advantage to being a screenwriter with acting experience. You can't complain when it's being done to your words because you know you've done that as an actor. Thornton still does that today when he acts. That doesn't mean as actors, they pervert the spirit of what's been written, but rather, they use their screenwriting knowledge to help improve the final product. There was a very long scene in a car, then there was a scene afterwards in an office and they were, for the most part, the same scene.