Ah, one of my favorite subjects: the comma. Just ran into this geeky ninety-second read from The Handbook of Good English. A cool study:
Don’t use a comma to indicate an understood word unless the sentence requires it for clarity.
His office gave him little satisfaction, and his wife, none requires the comma after wife so that the reader can be certain that something has been omitted there–a repetition of gave him. Without the comma, the sentence could easily be taken to mean His office gave him little satisfaction and gave his wife none. (The comma after satisfaction in the original sentence does not prevent this misreading, because it may be there just to give the second predicate a parenthetical effect.) Note that the comma after wife, required as it is, is really rather a nuisance; His office gave him little satisfaction, and his wife gave him none gives more satisfaction as a sentence.
He quit his job, and his wife, her excessive social engagements does not require the comma after wife, because the only possible meaning is his wife quit her excessive social engagements. We can take out the comma and still be sure both where a word is missing and what the word is. Since the comma has no function, it should be taken out.
He had always had a secret yearning for a more contemplative life, she for a life of toil and accomplishment requires no comma after she, even though the omission–had always had a secret yearning–is quite long.
He now has ample time to dream, she the self-respect of the breadwinner, they the loving marriage both had longed for, and I the suspicion that their solution would not work for us requires no commas to indicate the omissions, even though the omitted word changes form: she has; they have; I have.
The use of a comma to indicate an understood word or group of words is apt to make a sentence seem old-fashioned and fussy. If a sentence does seem to require such a comma for clarity, perhaps the sentence can be improved by supplying the omitted word or words or by otherwise changing the basic sentence to make the comma necessary.
