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Wiki on Serial Commas

There is no consensus among writers or editors on the use of the serial comma. It is nearly standard use in American English, but less common in British English

Arguments for and against

Arguments typically advanced for use of the serial comma by default include:

1. that it better matches the spoken cadence of sentences;[6]
2. that it sometimes reduces ambiguity;[7] and
3. that its use matches practice with other means of separating items in a list (example: when semicolons are used to separate items, a semicolon is consistently included before the last item, even when and or or is present).[8]

Arguments typically advanced for avoidance of the serial comma by default include:

1. that it is against much conventional practice;[9]
2. that it may introduce ambiguity (see examples below); and
3. that it is redundant, since the and or the or serves by itself to mark the logical separation between the final two items.[10]

Many sources, however, are against both automatic use and automatic avoidance of the serial comma, and make recommendations in a more nuanced way (again, see Usage and subsequent sections).

The article also says that many journalism style guides recommend against, possibly for saving space.

The Chicago Manual of Style, Strunk and White's Elements of Style, most authorities on American English and[citation needed] Canadian English and some authorities on British English (for example, Oxford University Press and Fowler's Modern English Usage) recommend the use of the serial comma. Newspaper style guides (such as those published by The New York Times, the Associated Press, The Times newspaper in the United Kingdom, and the Canadian Press) recommend against it, possibly for economy of space.

And finally

The differences of opinion on the use of the serial comma are well characterized by Lynne Truss in her popularized style guide Eats, Shoots & Leaves: "There are people who embrace the Oxford comma, and people who don't, and I'll just say this, never get between these people when drink has been taken."[12]

ETA:They also have better examples of ambiguity in both directions