In an interview with Jason Gorber of Moviefone, Desolation of Smaug star Evangeline Lilly revealed one of Peter Jackson’s nifty storytelling techniques:
“When you introduce a group of characters on screen, if you don’t introduce specific members of that group, nobody will care about that group. If you’re at war and that group is losing, they are the dispensable people, it’s only the people that you’ve been individually introduced to that you care about. Peter Jackson said that there is a three-minute window in a war scene, and if you don’t see one of your primary characters within those three minutes, you will have completely lost your audience. They will have tuned out and won’t care anymore.”
From “Evangeline Lilly on ‘The Hobbit’: I Didn’t Want to Be the Jar Jar Binks of the Trilogy,” posted December 12, 2013.