I am a strong believe that automation testing alone is not the way forward, we will always need manual testing alongside. It is too valuable to the SDLC (Software Development Life Cycle).
Most people would say that you can test things as a human would, however if you implement automation testing correctly, you should write your tests with that approach anyway.
Manual Exploratory Testing
For me exploratory testing is the most beneficial element to manual testing... This is where I believe the most amount of defects will be raised and it doesn't take hours to write, a user can simply just jump onto the browser, login and off they go.
The tester will also pick up on the little issues/defects that haven't been asserted within the automation test script. Yes this would be ideal that the script would test for everything, however in a commercial environment there are deadlines and you have to be realistic on providing a range of tests rather than one super detailed test that tests one particular functionality.
What do you mean by little issues/defects?
When I mention little issues/defects I am referring to the items that might slightly impact the users experience. This could be fonts, colours, headings, images, styling etc, all things that don't effect the overall functionality but the subtle details that enhance the users experience.
This is essential throughout the development phase (sprints) as it would not be cost effective to automate through these stages. Simply because projects can change very quickly and automating testing at this stage of the SDLC would just cost too much to maintain.
I am an automation tester and I honestly do believe in manual testing, both have their place within a project.