Screenwriters are often told to describe the set pieces in their screenplays. They help to sell the movie by giving the audience an overview of what your story is about.
A set piece defines a movie
The set pieces of a film refer to around five or six elaborate movie scenes or sequences that define a film both visually, thematically and dramatically.
Set pieces, rapidly define the stakes, conflict, climax and resolution. They anchor a film and hold it up like tent poles.
Set pieces refer to to the scenes of a film that are most innovative, memorable, tense and entertaining to the audience. They stimulate conversation around the water cooler in the office and appear in movie trailers and film reviews.
They are potent marketing tools since they contain the signature scenes which add unique elements to a film. That is why they are the keep components of film trailers.
They are considered to highlight essential thematic plot points which the film cannot survive without and advance key plot points. However, they must be well-spaced in a film to avoid losing their impact.
Since movie set pieces are so integral to a film, many screenwriters build the entire story around them. The interstitial scenes culminate to the set pieces, especially in high-octane action films.
Set pieces have their own three-act structure and can exist on their own as mini movies.
Set pieces vary according to genre. Consider “that” scene in “When Harry Met Sally”. It was vocal, unforgettable and funny. THAT scene has served as inspiration for countless other films.
That scene is perfect for this romantic comedy. As importantly, it defined the characters and theme of the film; namely whether men and women can really be friends. At the time it defined the mores of society, since men and women wanted to get married as soon as possible. It was a contemporary twist on the genre at the time.
How do set pieces differ across film genres?
A character drama might have a highly emotional scene which tugs at the audience’s heart strings at the expense of visual excitement. Thrillers tend to be laced with car chases, while horror has abundant gore, knuckle-biting and frights.
The key set pieces of “Titanic” occurred when the ship filled with water and sank. As an action film, the set piece had to be a pastiche that evokes visual and emotional stimulation in its audience.
Consider a key set piece in “The King’s Speech”; a crescendo, when King George VI makes his virtually stutter-free speech when war erupts between England and Germany. It is the pinnacle of the film, when King George VI overcomes his handicap, finds his courage and purpose and becomes a real king.
A major set piece in “The Social Network” occurs when Zuckerberg tries to friend his ex-girlfriend on facebook. Despite its subdued nature, it is critical to the movie because the socially inept guy creates a social revolution. His goal has been fulfilled and his character arc reaches its natural conclusion. Many films conclude with a set piece because it’s the last thing an audience sees before they leave the theater, assuming they leave without watching the credits.
In 127 Hours, the amputation defined Aron Ralston and his indomitable fighting spirit. Or even Jack and Rose’s doomed romance in “Titanic.”
So be creative and think visually about the key moments that comprise set pieces. This will also help you define key plot points in your screenplays and make you a better screenwriter. Yay!
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Gideon's Screenwriting Tips: Now You're a Screenwriter 
You’ve nailed the writing experience. One idea a movie makes. But properly fashioned set pieces breathe life into a smashing idea.
Life is what we do. Life must have subject and predicates. We see, feel, taste, hear, and sense our surroundings often throughout our day. However, we expect to be entertained with folks doing something facinating with their seen, felt, tasted, heard, and sensed time upon the screen we’re watching.