A playwright or screenwriter has considered as the most important part of the cinema crew because he is the one who describes the characters of the flick, gives a story to the production and writes up the dialogues for the actors. They work hand in hand with producers and directors. They know how to work in a team and give the best output even under pressure. They are the one who can make stories based on their personal idea or some pre-described concept. They are the one who narrate stories in detail and describes the characteristics of each every character carefully.
They may also need to produce a summary in front of the producer which includes several scenes from the story before the shoot and helps in developing them according to the shooting schedule. They also need to incorporate the ideas given by directors or producers. They also sometimes needed to create various versions of the script before finalizing one. So a screenwriter is the one who understand filmmaking, and also knows how to present their ideas in the script and knows the film language well.