Use of Narration in the Movie The Book Thief
The movie The Book Thief opens with narration by death, who adds some comments through the movie. In the film, a young girl is given up by her mother (who is possibly a communist or Jewish) to a German couple just before WWII. The girl is illiterate, but learns to read and then 'borrows' books from a local, well-off woman who lost a son in WWI.
I haven't read the book, but the movie has a golden-hued look that seems out of place with what is happening. The deeper problem is that, until the end of the film, it's not clear why it's narrated by death and what, ultimately, all the golden-hued action is meant to convey.
In the last line of the film, death admits to being haunted by the girl's death. To be a dramatic question for the story, the question of what about the death of her brother haunted the girl, and whether she could survive this haunting, would have given the film and death's narration a dramatic purpose. It's a question that would relate to other families in the film dealing with the deaths of loved ones in the war. But since this line comes at the end of the film, it's only then that the narration serves some dramatic purpose.
The reason people who write screenplays are told to NEVER use narration is that as a device, it lends itself to simply commenting on or explaining the action of a film, but not being dramatic unto itself. Narration as explanation, by its nature, tends to be dramatically flat; it's often the authors using characters to convey information the authors feel the audience needs.
An example of a dramatic use of narration is the film Days of Heaven, narrated by a young girl who doesn't understand what she's seeing, so her narration is dramatically interesting. What the audience sees happening is different that what she relates.
Another example of failed narration was in a horror film that was a remake of a Japanese horror film. In the movie, a new frequency is opened for cell phones, and via that frequency, the dead start returning to this world. The actors in the film all react to this event, but what the story is about is only revealed with the last line of narration, 'The dead had a stronger live to live than the living.' If that had been framed as a question at the beginning of the film, all the action would have had a purpose.
In films like this, actors are left to pose, because they aren't given characters to play. All the actors in The Book thief do a good job of posing, but they aren't given fully-realized characters to play.
Something else that's interesting about narration, even though screen writers are taught to avoid the technique, it's often used in popular films, Memento being a great example.
If you're going to use narration in a script, make sure it serves a dramatic purpose unto itself.