Editing: The editing is important in creating a trailer as this will give the audience the opportunity to see some of the best, most exiting shots from the film, not into too much detail, which will evidently make them want to go see the end product.
Sound: The music put over the editing on the film trailer will reflect on the genre this film is, for example a horror will have slow, anticipated scary sound, where as a action film would have a high, fast pace score in keeping with their genre's.
Notice the editing and sound used in this inception video above, used to make the trailer look the best in its certain genre and to make people want to go to the cinema to view the film. Without editing and sound this trailer would simply not wow audiences enough to want to go see a 'blockbuster' film.