Here's an example from Grammarly to show its importance:
I love my parents, Lady Gaga, and Humpty Dumpty.
That clearly means you are fond of of your parents, a pop star, and character from a nursery rhyme. But if you remove the Oxford comma:
I love my parents, Lady Gaga and Humpty Dumpty.
That could be read as saying that Lady Gaga and Humpty Dumpty are your parents. The Oxford comma can change the entire meaning of a sentence.
And in the case of a group of dairy workers from Maine, the course of justice.
Delivery drivers from Oakhurst Dairy in Portland have won a suit against their employer, after the judge ruled that the wording of Maine’s overtime rules were ambiguous.
The rules state the following activities are not eligible for overtime pay:
The canning, processing, preserving,
freezing, drying, marketing, storing,
packing for shipment or distribution of:
(1) Agricultural produce;
(2) Meat and fish products; and
(3) Perishable foods.
The company argued that “distribution of” was separate from “packing for shipment,” rather than just the activity of packing, for the purpose of shipment or distribution. This would mean Oakhurst doesn’t have to pay delivery workers overtime.
But the lack of an Oxford comma means it all reads as one task. So the court ruled in favour of the five drivers, and of grammar-lovers everywhere.
So when Vampire Weekend asked 'Who gives a f*ck about an Oxford comma?', we now have an answer - the US Court of Appeals does.