I know, I know, rules are boring. Rules are for squares. (Does anyone say "squares" anymore?) Rebels break the rules! Fight the machine! Sure...but let's face it, most rules are pretty good and work well. You know, "Don't take things that don't belong to you. Tell the truth. Don't touch other people without their permission." Yes, the basic rules our parents taught us from day one.
What about grammar and punctuation rules? Periods come at the end of sentences, indicating a stop. Sentences contain a subject and a verb and sometimes, adjectives, adverbs, conjunctions, clauses, pronouns, the possibilities are endless! Commas separate lists of "things" which could be grocery items, phrases, or clauses, encouraging readers to pause slightly between words. Colons often precede lists of "things" which are then separated by commas. Question marks indicate an ending tonal upswing when reading a line out loud. (For English speakers anyway.) I'm not even going touch SEMI-colons here. Those prickly twerps deserve a blog post all their own. Nevertheless, you get the picture. There are rules and you need to know them, intimately.
But! Some writers break those rules. Have you read Girl by Jamaica Kincaid? A gorgeous orgy of semi-colons, commas, hyphens, word repetition and one long, very long, run-on sentence. By formatting her piece in this manner, she effectively mimics the stream-of-consciousness monologue happening in an adolescent girl's mind. We don't think in properly structured sentences with perfect punctuation. Kincaid knows this and wrote this story accordingly, to prove a point. It is obvious she knows the rules and also that she breaks them with intention.
As writers, we are free to flout the dictates of grammar and punctuation WHEN IT SERVES THE STORY. We want our words to be authoritative, to represent our craft in its most perfect form. Unless we can justify our grammatical and punctuational choices within the story itself, those same choices undermine the narrative. Know when breaking the rules provides bang! or substance and when it just makes you seem stupid. Don't be the stupid guy.