I met with a prospective client the other day. It proved to be, shall we say, most interesting. She insisted that and should never be preceded by a comma, and could not be dissuaded from her view.
She was referring, of course, to the Oxford comma. It precedes the and in a list of three or more items. As its name suggests, it’s used in more formal writing. Example: her favourite dwarfs were Happy, Sleepy, and Sneezy. The Australian Government Style Manual suggests that you avoid using the Oxford comma, except where it aids clarity. So: her favourite dwarfs were Happy, Sleepy and Sneezy. To some readers, the resulting text is crisper. To others, it is a travesty of traditional punctuation. To me, it’s a question of applying a consistent style throughout the document. It’s up to you (or your publisher) to choose.
However, there are times when clarity demands an Oxford Comma. Example: for breakfast he ordered a grapefruit, a croissant, and bacon and eggs. For the purposes of this list, bacon and eggs is a single serving; without the Oxford comma, the sentence would look like a crazy person’s breakfast.
Even if you generally eschew the use of the Oxford comma, it does not follow that and should never be preceded by a comma. Our first responsibility as writers and editors is to make sense. If slavish obedience to a rule results in less-than-lucid writing, it’s time to discard that rule.