Rule vs Regulation

   Linguistically, all dialects are equal. The reason some dialects have more prestige than others is a social judgment, not linguistic.

   My words mean just what I choose them to mean -- Humpty Dumpty.

   A grammatical rule is a description of what users of a language or dialect actually do, not a prescription of what they must do. Unless, of course, they want to be perceived as part of a group with more social prestige. Then they should follow the guidelines of what others in the target group do.
   But if they don't care, it doesn't matter. Even so, people -- being the judgmental sort that they are -- will judge that the writer or speaker is part of a less prestigious group, and will treat him or her accordingly. That, however, is a social judgment, not linguistic.
   Conversely, if a member of a group adopts the speech patterns of a group that happens to have more prestige, he or she runs the risk of being called a snob.
   In some contexts, rules and regulations can be mandates, such as in law and in military codes of conduct. But in others, such as in language usage and style, a grammatical rule is merely a guideline to what many experienced writers and speakers regularly do. These guidelines are offered as a way of facilitating communication among users of the same dialect.
   In a way, it's a another code of conduct -- if you want to be accepted by others in the group, you follow the pattern of behavior and speech  adopted by the majority members of the group. That's part of the reason teenagers have their own jargon, or set of terms that only they use. And once their parents pick up and start using these terms, teens abandon them and invent new jargon. If nothing else, it's a way of showing their independence.
  All that being said, standards in grammar and spelling are important because they ensure accurate communication.