An excellent post on scientific research validating the TDD/BDD methodology notes one of the methodology's benefits:
Since the scope of a single test is limited, when the test fails, rework is easier.
In my opinion, this more than anything else is the benefit of TDD. How do you eat an elephant? One bite at a time. TDD sizes problems down to the smallest possible bite. It may be a journey of a thousand miles, but if every single step is buoyant, light, and easy, you'll be there before you know it.