In a large class it's easy for students to become passive. They take notes. Any teaching technique that can increase student interest and involvement can increase retention and learning. Demonstrations and dramatic devices can do just that. Demonstrations help students draw connections between abstract ideas and concrete phenomena.
Demonstrations also serve to interrupt the lecture.
In a large lecture hall, of course, passing around a moon rock or inviting students up to view white blood cells under the microscope is not going to work. The actors continue, with brand new accents and new ways of walking and relating. Greeley interrupts again several times with questions. When the reader's theater has finished, Greeley engages the class in a lively discussion, moving among the students, shooting out questions and pointing at answers. Then, quickly, a screen the size of Rhode Island lowers into the room, the lights are dimmed, and we watch Jane Fonda and and a costar act out the same scene we've just been talking about.