I don't follow TDD strictly, but I still think testing is important. I mostly see tests as help for future programmers (which includes the original authors), kind of like documentation. It's a rigid description of how the system should operate and therefore is usually helpful for refactoring or extending old code. I also don't doubt that many people go years without seeing utility in writing lots of tests. From my experience there's a lot of factors that go into how many tests you write before getting diminishing returns. Some off the top of my head: static v dynamically compiled lang, functional v procedural lang, age of project, etc.