I agree with Andre. The starting point isn't a tool. The starting point should be "how would I like to change the appearance of this photo?" Then you have to find a tool that makes that particular change. Often, there are several different ways to do it, some better than others.
I often find that once I have a general idea of an alteration I want, the first tool I pick turns out to be the wrong choice. Or, it does what I thought I wanted, but when I see the change done, I don't like it and have to go back to the beginning.
Or, to fit with Andre's example, one might start with something very general, not "I think the grass should be desaturated", but something more like "I want to emphasize the trees, so I have to make them stand out more from the grass." Then there are a number of options: changing tonality, changing saturation, lessening detail, etc.
That takes me back to the beginning. I thought Andre's crop was a big improvement. But you then desaturated the grass. My reaction was that doing this decreased the separation between the trees and the grass. I wasn't thinking at all about HOW you desaturated the grass.