Now, onto your question of what the point of archetypes is. I believe the point of these typical characters, settings, or themes are specifically up to each author. Different archetypes might be used for different purposes. For example, the mother figure might be the only archetype in a story, but her role is that of a guide, if you will. It could be that the main character needs that guidance. Hence, the mother figure.
So you see, the meaning behind the use of any archetype is much more specific than a broad, blanketed answer. Are there any specific references or archetypes you are wondering about?