Spielberg used it famously in Schindler's List, when Oskar Schindler enters a club to ID various SS men. It can be highly dramatic.
As the camera follows the actor, you rely wholly upon body language, subtle cues and the reactions of others to carry the story.
You can use a form of back acting in still photography, too.
What epic tale do you see woven into these three pictures?
Love and loss?
An attempt to comfort, summarily rejected?
A monumental case of halitosis?
(...or is he? The plot thickens!)