Sharpness control is a legacy from older technologies where adding edge information aided in perception of sharpness.
The modern display does not need the edge enhancement and adding such information detracts from the final image.
In the example the high sharpness setting adds alot of artifacts to the image, it is noteworthy that in some displays
the sharpness control can go into negative adding dark edging resulting in a softened image.
The optimun position is where the control neither adds or sutracts information which does not exist in the original image.