I have noticed in that in cases when listing certain things, the following convention is used

a, b, c, d and e

But I have also seen some cases where a comma is used before the and:

a, b, c, d, and e

Is there a specific usage case where such a convention comes to play?

marked as duplicate by Nathan Tuggy, user3169, StoneyB grammar Jun 10 '15 at 19:29

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