I guess it depends upon what kind of code you end up writing most. I tend to find lots of code I write has more complexity in the business logic sections than

I guess it depends upon what kind of code you end up writing most. I tend to find lots of code I write has more complexity in the business logic sections than the UI itself - there are lots of corner cases with no impact on the UI. I find automated testing (not necessarily TDD) adds a lot of value over manual testing in these scenarios. And the automated tests tend to pay off either at development time or after even a single change.