There are so many creative possibilities in software it’s hard to know where to draw the line, and it’s all to easy to over-process. It’s very subjective, and rightly so. What works for one person can leave others distinctly unimpressed.
There are some things that are usually best avoided: over-sharpening, over-saturation, awkward cropping, muddy tonal processing, unrealistic skies, and so on. Some global adjustments can harm the tonal balance of an image so it’s typically best to use tools to target specific areas, as the image above illustrates.