Grammar is not just about giving insight to language enthusiasts. By understanding the inner workings of language, a student can talk about literature and writing with much more precision and clarity. It gives students the vocabulary to interpret the author's intentions, literary devices, writing style, and more in a work of literature. A student's writing can also improve by use of proper grammar mechanics and writing conventions which have been modeled in the literature that they have studied.
While it is true that people acquire language naturally, to truly understand and use it effectively requires a working knowledge of grammar.