Research: Purpose of a trailer

The purpose of a film trailer is to entice fanatics to see the particular film which is being promoted.

http://www.movietrailers101.com/the-purpose-of-the-movie-trailer-a-quick-overview-for-new-readers/

What I have learnt from this article.

1. Editing has to show enough to intrigue the viewer, yet not too much which could potentially ruin the plot. The editing must strike the balance. 
2. Ensure that the tone and genre can be clearly identified so that the audience knows whether or not they want to view the film. 
3. Music is the most reliable way to make the audience feel they way us producers want to, so that they will want to see the film.
4. Taglines are becoming a more popular convention recently, more so than voice-over. 
5. Voiceover provides an explanation for quick shots shown in the trailer.
6. Trailer represent film artistry at the highest level.