Speed of editing

In films, a scene may last a few seconds, or it could last for several minutes on end. Depending on the length of the sequence it establishes the pace at which a film is happening.

The speed of editing will help to determine the mood of what is taking place on screen.

If the audience needs to feel anxiety and to be full of suspense the editing will indeed be very quick and the scenes and the shots will constantly be changing throughout the sequence. If the audience is to feel relaxed, the scenes would last a lot longer and would change less frequently. 

On the other hand however a film may not need any editing and could just be filmed in one constant take, however due to the lack of jumps the film may seem boring. 

However a trailer for a film needs to show what happens throughout the film in a number of minutes so therefore the editing will indeed be very fast. 

Scenes at the beginning of films need to help us see the story that is trying to be told throughout the film, so they must be long enough for us to understand what is going on throughout the beginning to get us used to the story, however as the film progresses scenes may become shorter due to the story becoming more developed.