Refactoring improves the design. What is the business case of good design? To me, it's that you can make changes to the software more easily in the future.
Refactoring is about saying, "Let's restructure this system in order to make it easier to change it." The corollary is that it's pointless to refactor a system you will never change, because you'll never get a payback. But if you will be changing the system‹either to fix bugs or add features‹keeping the system well factored or making it better factored will give you a payback as you make those changes.