In my experience, only a handful of people pay attention to comma placement. Also in my experience, those who do pay attention to comma placement (like me - go ahead and call me a dork) have VERY specific opinions about where commas do and do not belong.
The Oxford comma is the comma used after the second-to-last item in a list of three of more items. For example, in the sentence, "I went to the grocery store and bought milk, bread, and juice", the comma after "bread" is an Oxford comma. The Oxford comma is generally considered stylistic, meaning some guides require it and others do not. I believe the Oxford comma should be mandatory, and when I read any piece of writing that omits this (in my opinion) absolutely necessary punctuation, I can't help but both cringe and make the edit in my head. No list of mine will ever not include an Oxford comma.
Why do I care so much about Oxford commas, you ask? I honestly don't have a good answer for you other than that they help lists make sense and without them confusion often follows. Here's a good example:
Without the Oxford comma: I love my parents, Lady Gaga and Humpty Dumpty.
With the Oxford comma: I love my parents, Lady Gaga, and Humpty Dumpty.
No one's parents are Lady Gaga and Humpty Dumpty (although that would be fun, wouldn't it?), but it's easy to see how that misinterpretation could occur.
My mom understands my passion for Oxford commas, so she knew I would appreciate this article about how failing to use an Oxford comma came with a cost...in this case, to the tune of FIVE MILLION DOLLARS. That's right, failing to use an Oxford comma when describing when workers are exempt from overtime pay ended up costing a Maine dairy company a pretty penny.
So on this Monday morning, learn from their mistake and use your commas...and be grateful that not doing so in the past didn't cost you a few million dollars or Grandpa's life. 😉