I started my professional career performing manual user acceptance testing against customer facing websites over 15 years ago. I have had many roles where manual and exploratory testing are required in order to make sure that all systems are working harmoniously and without errors.
In my career I have found that automated testing is great at making sure that your system is behaving as expected from a user’s perspective. It is not very good at finding bugs unless someone has broken existing functionality. When new features are developed, having someone to design and execute tests is crucial for the following:
Human perspective – Sometimes development and design can get too far in the weeds and having someone to look at a new feature from the outside can improve the product
Adaptability – Requirements can change for any reason and for any time. Having a manual tester will allow for adjustments on-the-fly so that you can continue development without impediment.
Complex Scenarios – Sometimes features are very complex and automating them may not be reasonable. Having a tester create a detailed step-by-step plan may be a better option than investing a lot of cost into a single automation test.
Exploratory Testing – When a tester gets a new feature, they will likely first play around with it to see how it works, what does or doesn’t make sense, and provide any feedback or questions. The feedback that a tester can provide is very valuable as many times if they have difficulties understanding the feature, the user will as well