Not to be fractious, but isn’t grammar even more trivial than fractions? After all, fractions help you cope with 3/8 teaspoon of baking soda when doubling or halving your muffin recipe. Far more practical than cringing over offering guests less or fewer muffins. Readers are a novelist’s guests, and many simply couldn’t (or the inaccurate “could”?) care less. For many people, grammar evokes the nightmarish high school memory of diagramming sentences.
Admittedly, diagramming sentence won’t polish your prose. Still, the impracticality of that exercise doesn’t justify discarding the elegant system that grammar represents. Even if diagramming sentences won’t improve your novel, grammar certainly might.
Some folks lack it with language, just as others do with music. You wouldn’t inflict your off-key singing on a bunch of strangers, would you? Between “you and I” (sic!), consider protecting your readers from sounds that make them cringe. If the reader’s cringing, the reading’s not much fun.
Subordinate (“however, “but,” “if,” etc.) or coordinate (“and,” “also,” etc.) words indicate significance. Seemingly trivial word choices convey that some things are equal and others not. Intentionally or not, the clauses you create express relationships—including run-on sentences. Subordination captures causality at the sentence level: if the protagonist does this, then that happens. Doesn’t that deserve your attention? And your reader’s?
Grammar sensitizes you to what your sentence underscores. Aside from distance and wordiness, the real problem with passive voice is misplaced emphasis. If the bat is used by the girl, don’t you imply that the bat matters more than she does? Relationships between words (grammar!) accentuate or minimize. Noticing parts of speech encourages greater reliance on verbs instead of (yikes!) modifying everything with (sad) adjectives or adverbs (sadly).
Though part of syntax, this construction deserves separate mention. Grammar reveals whether you’ve missed an opportunity to connect, echo, and create unforgettable patterns. After all, what if Lincoln had said, “The government that represents the people, which is the one they help to run and is thus capable of giving them what is needed… “shall not perish from the earth.”