In Shakespeare the cross-dressing element is used only in his comedies. I did not find an example of cross-dressing in any of the tragedies and obviously not in the histories. So why does Shakespeare use cross-dressing? Well, because when used properly it can be very funny and Shakespeare knew how to use it. I also wonder if Shakespeare used it because his actors enjoyed it. Think about it, during Shakespeares time women acting was not acceptable. Thus teenage boys had to act the part of women. So if you where a teenage boy and had to choose between playing the part of Juliet or Viola/Cesario which would you pick? Well, my brothers picked Viola/Cesario. I like to think that Shakespeare put this element in because it might have made his actors more inthused about acting the parts. Mostly he uses it because it adds a great comic twist and who doesn't enjoy mistaken identity. However, today the whole element of cross-dressing can often make modern audiences very uncomfortable.