We do, actually.

An Oxford comma (or serial comma) is one placed before the coordinating conjunction (e.g. and) at the end of list. This was among the topics in the humorous Eats, Shoots & Leaves. The comma in the title, though not an Oxford comma, indicates how much a comma can affect the meaning of a phrase.

 

Consider this (probably apocryphal) book dedication:

"To my parents, Ayn Rand and God."

It is ambiguous, suggesting that Ayn Rand and God may be the author's parents. The addition of an Oxford comma removes this ambiguity.

"To my parents, Ayn Rand, and God."

This example illustrates clearly that the Oxford comma does have its rightful place. I will stress at this point, however, that not every list needs one. Indeed, some are better off without it. The mark of a skilled writer is to know when to include it and when to omit it.

 

Imagine that the author in question was not on speaking terms with her father and had omitted him from her dedication. It may have read as such:

"To my mother, Ayn Rand and God."

This is unambiguous, unless the reader assumes that the author's mother is both Ayn Rand and God. How would it look with an Oxford comma?

"To my mother, Ayn Rand, and God."

In this case, the addition of a comma adds ambiguity.

 

In summary, the Oxford comma is to be used with discretion, and ignored at your peril. The latter point is illustrated in a vivid and memorable (albeit risque) way in this article.