Primarily it's a way to build a model of a story's world, and two things fall out of that.

1. A wiki for the story. For the author and for readers, so you don't forget what happened 300 chapters ago, which promises are still active, and so you can explore a story you love structurally.

2. Translation. The system scales to millions of words, so when it translates chapter 100 it has the full, precise context of what happened in chapter 1, including speech registers, relationships between entities, and a synopsis of the world.

I read very long web serials myself, and I kept losing the thread of stories I loved. So primarily it's a way to build a model of a story's world, and two things fall out of that.