I disagree with Falstaff29.  It doesn't matter if the audience thinks in those terms or not, you and your actors should.  You all need to know more than the audience about the characters, what preceded the action of the play, what happens after the action and so on, so that you will know how to answer the questions Falstaff asks.  If the audience, say, is to be disgusted by a character's actions, what will precipitate that disgust?  Why is the character disgusting?  Does the character know he/she is disgusting? Do the other characters feel he/she is disgusting?  If you create a backstory, examine the "spine" of the play, you will understand better what you want your actors to do.  If you are the actor, you will have a better understanding of this person whose shoes you are standing in.

I will grant that there are many plays where such an examination serves no real purpose.  Maybe Harvey is one.  I played Elwood and, truth to tell, I gave a lot of thought to what had made him the way he is.  Perhaps another actor wouldn't need to do that or feel any motivation to do it.  I think it helps to decide some things for yourself, whether acting or directing.