What are the positive and negative effects of disguise in different works of literature?
Two works where disguise plays a prominent role are Shakespeare's Much Ado About Nothing and Sheridan's School for Scandal. There aren't too many mishaps in School for Scandal as a result of Sir Oliver's disguise, so let's start there. Sir Oliver comes back to England after a long time away and must decide about the character nature of his two nephews, Joseph and Charles, to determine to whom, one or both, to leave his riches. To make this determination--since he and his trusted estate steward, Rowley, disagree--he decides to disguise himself as a money lender and a poor relation and visit his nephews.
The disguised Sir Oliver has great success in learning about the true inner character of his nephews, and his two disguises are not discovered (he is a moneylender with Charles and a poor relation with Joseph). Therefore, there are only positive effects of disguise for Sir Oliver: he learns what he needs to know and bestows his money and blessing on the worthy one, Charles.
It doesn't go so well for Charles and Joseph however, though Charles is able to redeem himself in a wonderful way. First, Oliver catches Charles auctioning off the family art collection and portraits (the family being high-born and of long history) because he needs money. Yet Charles is redeemed when he won't sell his uncle Sir Oliver's portrait because of fondness for him and when it is revealed that Charles acted on behalf of a poor relation who needed money.
Joseph is found by Sir Oliver, disguised as a poor relation, while Joseph is in the midst of hiding a woman behind a screen because her husband stormed in asking if brother Charles is having an affair with her. All is revealed in the end. It is seen that Joseph is guilty and Charles innocently in love with Maria. Then Joseph curtly sends his poor relation (Sir Oliver) away empty handed and (apparently) in want. This is the negative effects of Sir Oliver's disguise: Joseph is condemned after revealing his true self though Charles is exonerated after doing the same.
Sir Peter--my Friend and Rowley too--look on that elder Nephew of mine--You know what He has already received from my Bounty and you know also how gladly I would have look'd on half my Fortune as held in trust for him--judge then my Disappointment in discovering him to be destitute of Truth--Charity--and Gratitude-- (V.iii)
Much Ado is more complicated. There are two primary instances of disguise in the play: (1) when a masque ball takes place and characters reveal secrets to others whose identities they have mistaken; (2) when Hero disguises herself as having died and thereby helps uncover the true villain in her near-tragedy. We'll talk a little about the second instance.
Hero is betrayed by Don Pedro's wicked brother when he has Marguerite disguise herself (another instance of disguise) as Hero and pretend to set up a romantic tryst with someone just before Hero's marriage to Claudio. Because of Marguerite's disguise and pretense, Hero is denounced at the wedding altar, abandoned and left to be rejected by her father and friends. The friar devises a scheme whereby she pretends to die and be buried so the truth can come out.
The positive effect of Hero's disguise is that Don Jon is exposed as the perpetrator of the deceit. He is denounced while Hero is exonerated. Another positive effect is that she is restored to her father and her good name. Another is that she forgives Claudio and is married to him with joy and blessing. The negative effect is that the scoundrels are exposed and justly punished.
One Hero died defiled, but I do live,
And surely as I live, I am a maid. (V.iv)