> Everyone understands the idea, it's just a massive time sink for no more benefit than a test-after methodology provides.

This is not something I agree with. In my experience, when TDD is used you come up with solutions to problems that are better than what you'd come up with otherwise and it generally takes much less time overall.

Writing tests after ensures your code is testable. Writing your tests first ensures you only have to write your code once to get it under test.

Again, you don't always need TDD and applying it when you don't need it will likely be a net time sink with little benefit.