Automation is mostly employed for regression, i.e. to gauge the impact of changes on ‘already-working’ functionality. The same Manual test cases are automated and executed. Automation is for confirmation. What if you want to find issues/defects? Yeah! Manual testing is the first approach. After all, end-user is not a scripted machine. Simulating end-user behavior, testers explore the application with some alternate flows & on-the-fly data.
Different tools serve different purposes, the selection of tool should be done on the basis of your project requirements and application under test. Whatever tool you pick, it should empower you in achieving your automation testing goals.