Some of the drivers of these changes may be outside of management's control. A recession in the economy could push sales down for all companies, for example. But other factors at play could be within management's control and should be analyzed with a critical eye.
For instance, if revenue exceeded expectations, management can use variance analysis to drill down into why revenue outperformed. Perhaps it was an improved marketing strategy, higher prices, or a new product release.
On the expense side, the same logic is also true. If the company's marketing spending exceeded the budget, did that higher spending translate to higher sales as well? Or perhaps expenses rose after opening a new location, but sales didn't rise as high as anticipated. In all of these cases, variances point to places where reality didn't match expectations. It's in those cracks where management can learn and improve.