http://www.slate.com/articles/arts/film_school/2015/06/how_filmmakers_use_tracking_in_and_out_during_monologues_to_great_effect.html

When filming a monologue, directors sometimes decide that frequent cuts back and forth or a perfectly still camera are not enough to bring the scene home. Instead, they may favor a different technique: pushing or pulling the camera in at a steady pace. You may not always notice it as it’s happening, but the device has been used during countless monologue sequences to great dramatic effect in everything from Citizen Kane to Good Will Hunting.