I think it depends on your development environment. If you're writing something small and it's just you, you'll understand everything that you're doing (hopefu

I think it depends on your development environment. If you're writing something small and it's just you, you'll understand everything that you're doing (hopefully). If you're building a complex system with multiple parties and you're practicing separation and rotation of duties (no one owns any piece of code), then YES. I've gotten to the point that even for interviews where I'm asked to write code, I'll add test cases into whatever I'm building. I've worked on projects where code isn't tested and I've made a simple change thinking that's all I had to do to fix some "bug" only to find out by the QA team that I've broken three other features. Features which test cases would have been able to spot at build/test time. This took an hour fix and turned it into a week long back and forth with QA and the original developer. On the other side, I just wrote an iOS game and it has 0 test cases. I pretty much know what's going on, I'm the only developer on the project and I don't see it getting much bigger (famous last words right?).