This is a practical technique for shooting a scene in a studio with less space than might be required. How can that happen? Isn't the size of a studio pre-determined by the number of sets scheduled to occupy the space? Initially, it is. Then any number of things could happen: the schedule changes or a critical location is lost or an additional series of shots are added to forward the storytelling. At that point, a forced perspective set might be squeezed into the empty space previously occupied by assets already shot and wrapped.