Recently, @APStyleBook@twitter.com (henceforth, AP) was criticized much after posting a 9 tweet thread explaining their usage of the #OxfordComma (henceforth, OC). Criticism was for the length of explanation (9 tweets!) by those who don't see the grammatical role of OC. Essence of AP's guidelines, given with examples of usage, is two rules:

1. Do not use OC in simple series or anywhere else where it is not needed to bring clarity or accuracy. (the "no OC rule" of AP)
2. Use OC in complex series, where the final phrase of series includes a conjunction, and wherever it brings clarity.

Philosophy behind these is encapsulated in general rule for punctuation: Use punctuation that is needed; don't use what is not needed.

Missing was a demonstration of how blatant ambiguities arise if OC is used everywhere without discrimination. This, I indicate here by borrowing examples given by @svenosaurus@twitter.com :

... If "I want to thank my parents, Ayn Ran and God" is confusing, then so is "Donald will be accompaid by his three nephews, Huey, Louie, and Dewie."

NOTE ON CONSISTENCY OF OXFORD COMMA

The "do not use OC" policy misses the point entirely, while the "use OC everywhere" policy misses is that without AP's "no OC rule", OC in itself becomes totally pointless, while it serves a useful, even essential, grammatical function if used as per AP style. Thus, consistency for OC renders it useless and serves no purpose.