The particular scenario in the article is one in which denormalizing would be not only more efficient, but more correct as well. As the author points out, an in

The particular scenario in the article is one in which denormalizing would be not only more efficient, but more correct as well. As the author points out, an invoice should always reflect the order at the time that it was created, not including any subsequent changes in pricing. However, this is strictly a matter of correctness! In order to denormalize, it should either be demonstrably more correct (in which case it is not technically denormalization at all), or a significant performance bottleneck where the cost of maintaining two copies is overshadowed by the savings. Doing so in the name of performance without any proof that there's savings to be had is folly.