Perhaps out of all the controls that digital imaging put into the hands of today’s photographers, sharpening has been most widely abused.
The reason for this is that sharpening is a subjective impression and not a measurable detail of the photograph. A high-contrast image, for example, tends to look sharper at a glance than a photograph with muted tones. There is also no good measurement of sharpness. Most evaluations are in terms of “too sharp” and “not sharp enough.” This isn’t to say that these are poor descriptions, just that they don’t transfer well from one viewer to another. It reinforces the principle that the photographer should make the judgment.
The factors that give an impression of sharpness are acutance, contrast, resolution, ...