I'm told that it's more efficient to leave your central air conditioner running continuously?

Maybe it is, maybe it isn't. I live in the hottest city in the nation and it only takes one night to cool a house to the desired temperature. If you live in a moist area you might want to keep your ac or at least a dehumidifier running all the time to control mildew. In winter you absolutely need to keep your entire house above freezing at all times.

You may have some other considerations. There is no strict answer for all people.

"Efficient" does not apply. You are talking about cost of power versus cost of consequences.