“Comma jockey” is one of the derisive terms by which copy editors are sometimes described. But if we don’t ride them, who will?

The problem with commas is that they serve two distinct functions that are easily confused.

Some commas serve essential syntactical purposes, such as marking the beginning and end of an appositive phrase. Omitting one of them can confuse readers and force them to back up, making that distracting beeping sound.

Some commas are purely discretionary, representing the writer’s sense of where a pause should fall, particularly in the representation of spoken language. In this understanding, punctuation is analogous to rests in musical notation: the comma an equivalent of an eighth note, a semicolon a quarter note, a colon a half note, and a period, or full stop, a whole note. 

This is the kind of comma that James Thurber describes, explaining why Harold Ross, the editor of The New Yorker, would countenance a comma in the sentence, "After dinner, the men went into the living room." Thurber, in The Years with Ross, says that the comma was "Ross's way of giving the men time to push back their chairs and stand up."

Any given text is likely to display both functions of the comma.

What is a little bewildering is the tendency of many writers to omit the comma where it is necessary to mark the separation of independent clauses and to insert it in compound predicates where it is unnecessary.

In The reporter completed his story in good time, and his editor moved it to the copy desk in good shape, the comma before the coordinating conjunction and is essential for syntactical purposes. In The reporter completed his story in good time and left a number at which he could be reached, there is no grammatical need to insert a comma before and, though many misguided writers would. 

As for the dreaded-in-English-classes comma-splice run-on sentence, in which two independent clauses are linked by a feeble comma rather than the sturdier semicolon, British writers are addicted to it in all contexts, and American writers favor it in the representation of speech. All others, beware.