Unit tests are a great way to have a clear and reliable code base. Good unit tests gives you the confidence that your production code is doing what is designed for and helps to prevent regression when the code is modified. This is why you should write clean, clear and reliable unit tests by putting in practice the unit test best practices like those presented in this tutorial.
Unit tests should also be part of your Continuous Integration (CI) process if you have one. A Good CI process should systematically run unit tests and provide the development team with reports containing valuable metrics like code coverage, coverage on new code, number of tests being run, performance etc.