Think that regular people don’t care about punctuation?
Think again.
A friend from high school recently posted this on Facebook:

Lauren’s grammar homework:
Choose the correct way to rewrite the end of this sentence: “A string quartet has two violins a viola and a cello.”
a. two violins, a viola, and a cello.
b. two violins, a viola, and, a cello.
c. two, violins a, viola and a, cello.
d. no change is needed.
Maybe I’ve spent too much time with my AP Style Book, but none of these are correct!!!

Thus began a heated debate over commas, with 81 comments posted by a variety of people over less than two hours—and more comments to come.
The original post was by a career newspaper journalist. Journalists use Associated Press (AP) style and are firm in the belief that the serial comma is superfluous and must be expunged.
I was once a newspaper reporter and editor, so I remember my distaste for that “extra” comma.
But then I started editing for an assessment test publishing company. Educational publishers favor the serial comma.
And then I started editing proposals for tech companies that have corporate style guides based on Government Printing Office (GPO) style, which calls for serial commas.
And then for five years I was immersed in book publishing. Book publishers have corporate style guides based on Chicago Manual of Style (CMS), which also calls for serial commas.
Today, for nearly everything that goes through Dragonfly Editorial, we use serial commas. That’s because most of our clients use styles based on GPO (for tech editing) or the AMA Manual of Style (for medical editing). Both dictate use of the serial comma.
After five years of deleting those commas and 10 years of putting them back in, the serial comma and I have become friends. I appreciate its ability to clarify where one item in a list ends and another begins—which can be difficult to discern in the technical material that we edit.
But whether I like the serial comma or not isn’t important. What is important is knowing what the client wants.
In the latest edition of The Copyeditor’s Handbook, author Amy Einsohn touches on the debate:

The other issue concerns the so-called serial comma, which is the comma before the and or or that precedes the last item in a list. Chicago, WIT, APA, and CSE all either require or strongly recommend the serial comma, but most newspapers and magazines use the serial comma only when needed to avoid ambiguity. Ask your editorial coordinator about house policy.

And so, we can agree to disagree. And any time I go back to newspaper or magazine writing, I better be ready to check my “extra” commas at the door.