Montage reel

Here are a few examples of cutaways in a montage. They can make up a large majority of a film to add extra scenes to either fill or add to the movie. It cuts away from the main action or sequence of a film to a separate or secondary action. However, for continuity you need to make sure the cutaway does link to the action to enhance what you are watching and sometime even adds more to the film than if it wasn't there. 

As said before, cutaways aren't necessary but they do help sometimes in adding to the final product of the film so it isn't as monotone and uninteresting. They can, however, be boring and do nothing for the film if they aren't used correctly.