Currently we have about 80% test coverage in fairly large (and growing) react/redux application. The major benefit for us is when we refactor or integrate new code. Our build process lints and runs our unit tests so that we know if some change broke code that was written months ago.
If your project is small, doesn't change often or doesn't have a team working on then I can see how it would be tough to see the benefit but it exists.
Tests are a great way to document the behavior of code. If you bring on a new team member who wonders how the application functions it's pretty easy to discern that from the tests.