I love starting a new project notebook for a new project. I like to make entries for all the characters: protagonist, antagonist, love interest, side kick, etc. And then I do my favorite step of all: I find pictures of the stars I want to play my characters. Like all choices in screenwriting, this approach has its proponents and detractors. These reasons are why I like it, with a few reservations.

Casting keeps things realistic.

Your protagonist should be based on an actual star. You can write a part for a young Dustin Hoffman, but barring a time machine, you’re not getting him. Instead, consider movie stars who have successfully carried actual in the genre you’re writing in the last year, then tell your story using them. This keeps your script in the realm of the plausible, your spec probably won’t get made, but keeping it castable will save it from setting off the bullshit detectors of cynical, savvy script analysts.

For extra credit, look at the kinds of movies and the kinds of budgets your ideal star works in, and then look at how they’ve been doing. If Ryan Gosling has ten flops in a row, his cachet as an inspiration may diminish. If William Hung suddenly becomes the hottest box office star in China, he may be worth considering. Examining movies from this angle gives you a hint of what life is like for studio execs, who have to play this fame vs. cost game of fantasy football every day.

Don’t cite your casting inspiration in your actual script.

Your casting is for you too understand your own material, not to use as a shorthand for others to see your world. You don’t want to lose out on opportunities because you call your black cowboy a “Will Smith-type,” only to inadvertently offend Jamie Foxx.

“Casting” frees your imagination for other tasks.

Contrary to what Albert Einstein may have said, imagination is finite. You only have so many cerebral resources to devote to the task at hand. It’s tough to render a fully realized character in your head, to truly envision their face and manner. It becomes even tougher when you juggle this image alongside all the action, dialogue, choreography and scene description that you’re going to have to keep track of while you’re writing your scene.

If you cast bad guys 1, 2, and 3 as Vinnie Jones, Ray Park, and Jet Li, tack up their pictures to your board. Externalizing the visualization will free up your mental resources to work on other details, like plot, arc, tone, and setting (though so long as your finding pictures, you could also grab one of your dream setting).

Casting locks you into specificity.

Many writers like to keep things open. Rather than making a strong choice which might be wrong, they keep things vague. Rather than say the bad guy is a tall Chinese woman or a short black man, they’ll keep it open, like a variable in a computer program. The urge to keep things loose is understandable, but ultimately the variables overwhelm the fabric of the script. It’s better to make a strong choice, be wrong, and then make another strong choice than it is to avoid making the decisions. Writing is about making tough choices. Choosing option A over option B. You’re writing a script, not a Choose Your Own Adventure novel. When you cast your secret agent protagonist as Tom Cruise, you are definitively stating that he is a Tom Cruise type, not a Brad Pitt type. You can always change your mind. A wrong decision will teach you more than being afraid to make one at all.

Casting helps dialogue.

A client had trouble writing a scene between a father and daughter. I pitched Tracy Morgan and Joy Bryant, and suddenly the scene began writing itself. Ultimately she went with Gabrielle Union and Denzel Washington, and that was funny in a completely different way. “Casting” gave her permission to explore different kinds of lines for her characters.

Sometimes competence is just a matter of knowing the right protips that will help in certain situations. Casting is not a magic bullet and it might not be for you, but it’s worth keeping in your toolbox for the times when it can get you unstuck.