An opportunity to showcase your idea, event, business or product in more than one dimension, for the consideration of people as if they were browsing in a museum. Up close and personal. Usually in a conceptual, creative way. Lure their attention and then hold it. Tell them something that just might change their lives.
Also, these things can travel. Durable enough to be reused, yet cheaply enough produced to change as often as needed. Really the best of both worlds.