Recently there was a back-and-forth in a indie author group about whether or not to use the Oxford comma. Some of it was kind of funny. One person asserted that when she sees someone use the Oxford comma, she assumes it's someone over 60. I posted a link to a FiveThirdyEight post on a survey that showed that younger people prefer it by a wide margin over the 60+ group. So she said that's only a U.S. thing. Evidently in New Zealand, only old people use it.
Well, okay, I give up. I'm not going to go searching for a funny post about the Oxford comma in New Zealand.
But to tie things up, I proposed that young people probably prefer it because they are no longer fettered by the restrictions of pre-computer typesetting and printing, where eliminating some commas might save some print space – kind of like the old two-spaces-after-a-sentence thing, which was a way to avoid readability problems caused by monospace type fonts (and which is not useful at all in the digital age).
I want to propose a writer's approach to making decisions on this kind of thing, not to hammer on the Oxford comma per se, but here's my take on that, just to get it out of the way:
It's purely a question of clarity. The purpose of using the Oxford comma is to avoid ambiguity in lists. I won't list famous examples of sentences that fail by leaving it out; there are tons of posts on that.
Here's my suggestion for writers, on choosing sides on form/style/punctuation/structure issues: Try to take your habits and personal preferences (which typically are also just habits) out of the picture. Don't try to justify what you're doing now. Instead try to evaluate the thing independently of your writing, or anyone else's writing.
Ask the simple question:
Why should I use or not use this particular element?
Here are some specific examples that strike me as bad responses:
It's a matter of personal preference, or writing style. Well, purely as a matter of fact, sure. You choose one structure or another. Something gets written; there it is. But that doesn't answer the question. Usually this response has an included assumption: Either one is fine, and I choose this one. But there's almost always a substantive difference. It's not random. To say that either is fine is to fail to understand the difference. Whether it's the Oxford comma, or splitting infinitives, or whatever, your writing is going to come of differently depending on your choice.
Readers don't care about this. This is a variation-on-theme of the personal preference objection. Readers might not think, "Wow, I hate/love the use of the Oxford comma here," but the overall impression of your writing is affected by all the decisions you make (or don't make) about the elements of writing. Each one, individually, makes up part of that.
Less is more. I like this, as a general mantra in writing. But less is only more if the result works. If your sentence is ambiguous, it's not better.
My writing teacher says everyone should do it this way. Argumentum ad auctoritatem. I'm inclined to tell people to listen to what their writing teachers have to say, but on any given point, your writing teacher might be right, and might be wrong. The question is, why does your writing teacher say everyone should do this?
More people do it this way. Or: My peers all do it this way. The herd mentality is a powerful draw, but sometimes the majority is wrong.
In my own writing, I've changed how I do a lot of things. Often it's because someone says, "You're doing this wrong!" and either gives me a good reason, or just asserts that it's the wrong way to do it. I find either one to be enormously helpful. Even if the reader can't put a finger on the reasons, if something stands out and bothers the reader, I want to know. Then I can consider the rationale behind one form vs. another, and decide which is best.
I could also stubbornly refuse to change it, asserting that it's my personal style, or I like how it looks. But my readers don't give a damn about what I think of these things. Not to consider elements of writing style independently of my preconceptions about them (or ignorance of them) is to miss out on something that could help me improve my writing.
Image reference: New York Times story about a legal case in Maine that hinged on the lack of use of the Oxford comma. See the story here: https://www.nytimes.com/2017/03/16/us/oxford-comma-lawsuit.html