A lot of work goes into creating a video or film production, no matter what the final length. There's research, writing, planning, casting, scouting, prepping, delegating, rehearsing. All this before a camera even gets switched on. After shooting begins, hours of footage may be accumulated, all for the editor to piece together into a coherent and interesting completed work.
This article by Adam Fulfurd is a nice overview on the art of film editing. And it truly is an art. Poor editing can dramatically change the entire production, negating all of the hard work and planning that occurs before the cutting room.
In a sense, the editor gets to play God, choosing who, what, when, where, and how content will be revealed to the audience. This is a lot of power, and with it comes a large responsibility: to make the best choices that push the story forward in the best way.
When choosing a production company for your project, knowing who will be editing the final cut is vital. Make sure to view any editor's reel, or better yet a couple of their works in their entirety, before making a decision. Also, does their style lend itself to your project? After all, you most likely wouldn't commission Salvador Dali if you were wanting a finished piece to resemble a Renoir.
As Adam mentions in his article, editing isn't just a mechanical, techie-type job. It's a craft.