dramatists had to take into account costs and difficulties and expenses of changing scenery
expected to limit settings to a few= change of scenery= new act
explains why Williams a-typically limits his play to 11 scenes with no break for an interval indicated
no change of scene= pointless
also, increases the dramatic tension= each act ends with a dramtic punchline or gesture= if the play was broken up into 3 acts (as conventional) the audience might become less absorbed in the action as each break would effectively take them out of it