Automated Unit Testing is a powerful technique in driving code quality and improving confidence in the code.
Developer Unit testing takes up your precious time, that could be used for getting more coding done, or could be used for more involved testing that really needs a human.
Automated Unit Testing by definition, works for free and in parallel with your day to day tasks.
Once you have used it, it is really difficult to go back. Without Automated Unit Tests there are developer activities like refactoring that you simply cannot do safely. You can afford to take risks during feature development, because you are more confident that unintended consequences can be captured.
I would never by choice commence another project that didn't inherently use automated unit testing.