"A Modest Proposal"--Link
Commas are indeed one of those things that matter ... in print, of course, not in oral language. Every now and then you can be waggish and actually speak the word comma in one of your sentences, but for the most part we tend not to. It's a little bit show-offy, even elitist, I would suspect, to mention all the punctuation marks as you speak. Imagine Lincoln at Gettysburg:
Four score and seven years ago our fathers brought forth on this continent [COMMA] a new nation [COMMA] conceived in Liberty [COMMA] and dedicated to the proposition that all men are created equal [PERIOD]
Actually, Lincoln's commas are kind of odd, aren't they? If a student were to submit a sentence like this, I would remove the comma before a new nation ... wouldn't you? I'd make Lincoln rewrite that sentence ten times, just to make sure he knew not to put a comma between the verb and its direct object. (Maybe he was absent the day they covered that rule back in his Illinois school?)
Of course, we invented all punctuation marks and the rules for them. To a great extent they're arbitrary. And they change over time. Fashions in punctuation change with hemlines. When you read Victorian novels, you notice, for example, that those writers liked to use dashes and commas side by side. In Emma, Jane Austen wrote,
"In the meanwhile the lame horse recovered so fast, that the party to Box Hill was again under happy consideration; and at last Donwell was settled for one day, and Box Hill for the next,--the weather appearing exactly right" (Oxford Illustrated Jane Austen 357).
Nowadays, most writers wouldn't punctuate as Austen did in that passage. Some might put a comma after meanwhile; many would have a comma, not a semicolon, after consideration; many would not put a comma after day; and no one would put a comma and a dash after next.
I'm not advocating chaos by comma, however. Clarity is always the issue. (We don't want grandmothers being served for Easter brunch.) I still like the rule about commas and compound sentences, commas with nonrestrictive modifiers, nouns of address--that sort of thing. I like the judicious use of the semicolon, the colon; I'm in love with the dash--really. I hate exclamation points! Absolutely hate them! Especially multiple ones!!! And I hate starting sentences with conjunctions. But they're not as bad as sentence fragments.
Which I never use.
(And avoid parentheses.)
(And have you noticed? Commas look a little like sperm. Another reason to use them judiciously.)