Michael Swart shows how reversing index sort order can expose invalid assumptions in code:
Remember that this is an application problem and is not a SQL problem. We only get into trouble when applications (or people) expect results to be sorted when they’re not. So unless you have a tiny application, or a huge amount of discipline, it’s likely that there is some part of your application that assumes sorted results when it shouldn’t.
Here’s a method I used that attempts to identify such areas, exposing those assumptions. It involves reversing indexes.
It’s an interesting idea to try out in a dev environment.