Refactoring Helps You Find Bugs
Help in understanding the code also helps me spot bugs. I admit I'm not terribly good at finding bugs. Some people can read a lump of code and see bugs, I cannot. However, I find that if I refactor code, I work deeply on understanding what the code does, and I put that new understanding right back into the code. By clarifying the structure of the program, I clarify certain assumptions I've made, to the point at which even I can't avoid spotting the bugs.
It reminds me of a statement Kent Beck often makes about himself, "I'm not a great programmer; I'm just a good programmer with great habits." Refactoring helps me be much more effective at writing robust code.
Refactoring Helps You Program Faster
In the end, all the earlier points come down to this: Refactoring helps you develop code more quickly.
This sounds counterintuitive. When I talk about refactoring, people can easily see that it improves quality. Improving design, improving readability, reducing bugs, all these improve quality. But doesn't all this reduce the speed of development?
I strongly believe that a good design is essential for rapid software development. Indeed, the whole point of having a good design is to allow rapid development. Without a good design, you can progress quickly for a while, but soon the poor design starts to slow you down. You spend time finding and fixing bugs instead of adding new function. Changes take longer as you try to understand the system and find the duplicate code. New features need more coding as you patch over a patch that patches a patch on the original code base.
A good design is essential to maintaining speed in software development. Refactoring helps you develop software more rapidly, because it stops the design of the system from decaying. It can even improve a design.