Automation testing is useful for regression, smoke or sanity testing. All these types of testing in the traditional waterfall model happen at the end of the cycle and sometimes if there are not many enhancements to the application, we might not even have to do regression testing.
Whereas, in agile methodology, every iteration requires executing the regression test case as some new functionalities is added.
Also, the regression suite itself keeps growing after each sprint as the functional test cases of the current sprint module need to be added to the regression suite for the next sprint.
Thus, Automation testing in agile methodology is very useful and helps in achieving maximum test coverage in less time of the sprint.
