It's a useful tool, because by revolving your story around a narrative theme, you can solve many problems at once. Most obviously, this gives a moral to your story - it makes your story make a point. The way that the protagonists deal with the theme is the way you believe the theme should be dealt with in real life. Having a narrative theme also helps your characters' interpersonal dynamic: by design, your characters will have similar histories and that will give them a way to relate to one another. It will give protagonists a way to build rapport and camaraderie, letting them understand each others' struggles. Similarly, it will make your antagonists' motivations relatable to both the audience and the protagonists, while also playing upon an irreconcilable difference between the way your protagonists and antagonists deal with the theme. The antagonists' improper or unhealthy way of dealing with the theme can also cause the protagonists to consider their own motivations and strengthen their resolve.
I think of using a narrative theme similarly to how I think of the standard five paragraph persuasive essay format that many of us learn in school. It has its drawbacks and may be seen as overly formulaic to the trained eye, but it's also a very good way of learning the fundamentals of the medium. Using a narrative theme doesn't seem quite so amateurish to me as a five paragraph persuasive essay, but I say this as someone who isn't yet accustomed to creative writing.
I may go into more detail on this in future posts, but here are the themes that I noticed in some of the Final Fantasy games:
- Final Fantasy VII - Dark pasts
- Final Fantasy VIII - Love
- Final Fantasy IX - Identity
- Final Fantasy X - Death
- Final Fantasy XII - Loyalty (not as sure about this one)