One advantage of a stereotype is that it enables us to respond rapidly to situations because we may have had a similar experience before.
One disadvantage is that it makes us ignore differences between individuals; therefore we think things about people that might not be true (i.e. make generalizations).
The use of stereotypes is a major way in which we simplify our social world; since they reduce the amount of processing (i.e. thinking) we have to do when we meet a new person.