Not to pick a nit, but shouldn't it be "using bad grammar?"
Ok, here's my two cents. Grammar IS important, but largely because of how you or your writing will be perceived if your grammar is incorrect. There are a lot, a LOT of language/grammar snobs out there who will jump all over you for using bad grammar, or who will use bad grammar as part of a "see what's wrong with these kids today" screed. The truth of the matter is, language (and grammar) changes with usage. The evolution has slowed down considerably with the advent of mass communication, but it still does change over time. Language is a living entity; we do not, and cannot, impose rules on it, we can only observe how it behaves.
Your guiding star should be clarity. Conventional, mainstream grammar will make your writing clear and understandable. It is for this reason, and this reason alone, that grammar is important. Rules, however, can be broken.
For those to whom English is a second language, don't feel bad if many of the rules are challenging. Modern English is the second youngest language on Earth (Swahili is the youngest), and it, and its rules, is a composite old Germanic and French languages. Composites are always troublesome.
A few bits of trivia: did you know that "ain't" is a contraction of "am not," and used to be perfectly acceptable? Did you know that nearly all of the "vulgar" words in English are vulgar not because they're scatological, but because they're Saxon words, and were labelled vulgar by Normans when they invaded England? Did you know that the rule in English about not using a double negative was imposed on us by a mathematician, who felt that if two negatives make a positive in mathematics, the same must be true for language? Interestingly, despite this rule, English speakers still use double negatives, informally anyhow, in the same way Chaucer, and writers before him, used them: for emphasis.
edited 16th Oct '12 3:22:15 PM by Robbery