It allows you to refactor your code and tell whether or not you have changed behaviour. This is practically what unit tests are for full stop. It also allows y

It allows you to refactor your code and tell whether or not you have changed behaviour. This is practically what unit tests are for full stop. It also allows you to modify behaviour and show that the behaviour has been modified as you expected without writing any additional tests. If you are finding them too brittle, then you can remove the ones that are bothering your and replace them with better tests. It's a very good technique that I've used many times in the past.