Sometimes this is the only way to let the audience in on something, but no, this isn't the purpose of dialogue. It should move the story forward, but no this is not it.
Conflict is very important, but no.
Dialogue may do all of these things, but these are not what dialogue is for. Dialogue is your character's reaction to other characters, and the purpose of dialogue is communication between characters. Make Your Characters Say Something When someone says something to another person, unless he is just making conversation, he wants the other person to react to what he is saying. Bill wants Paul to be impressed with him, to leave him alone, to give him money, to let him do something, etc. When Paul hears something from Bill, he reacts.