This article by Dan Selakovich makes the strong case for why films benefit from a skilled editor, separate from the director:

http://www.watchindie.net/2015/10/27/why-a-director-shouldnt-edit-their-own-movie/

It boils down to objectivity, to getting away from all the baggage of remembering what happened on set.  He makes a compelling case, and his advice is the conventional wisdom.  It reminds me of WIlliam Faulkner’s advice on editing yourself: “In writing, you must kill all your darlings.”  He meant that you need to let go of your attachment to any one little bit, to focus on the needs of the story.

And yet…  There are quite a few noted filmmakers who edit their own work.  The Cohen brothers spring first to mind.  But also Akira Kurosawa and Gus van Sant.  And quite a few documentary filmmakers edit their own work, although perhaps as much because of a lack of budget as from creative considerations. Here is a short list of filmmakers who edit:

And So It Begins list of directors who edit

Any thoughts?  I edit to learn, and will hire an editor when I can afford to.