Hosley, Richard. "The Use of the Upper Stage in Romeo and
Juliet." Shakespeare Quarterly 5 (1954): 371-379.

Thesis: In order to follow Hosley's argument you must remember this about Act 3, Scene 5: After Romeo and Juliet say their final farewells, Juliet's mother enters Juliet's bedroom, followed shortly by Juliet's father and the Nurse, making a total of four people in Juliet's bedroom.

Four is too many.

If you imagine the "balcony" of the balcony scene as being at 12:00 o'clock in the almost-round Globe theater, those seated between 10:00 and 2:00 would have a great deal of trouble seeing anyone who wasn't leaning on the railing of the balcony. (By the way -- in the play it's consistently referred to as a "window," not a "balcony.")

Hosley argues this point at length, and argues against certain scholars who asserted that the upper stage space was used extensively for interior scenes. In the process, Hosely defends the rightness of the rather peculiar stage directions of Q1 (scholars' name for the first printed copy of Romeo and Juliet); those stage directions indicate that after Juliet says farewell to Romeo she descends to the main stage, which then becomes the interior of her bedroom, even though the window of her bedroom is one story above.

Bottom Line: It's pretty obvious that Hosley is right, and therefore his essay seems a bit tedious.