It's one of the main things I strive for in my photographs, especially in wildlife photography. To have clear separation between wildlife subjects, between a wildlife subject and the elements in the background, and even how a wildlife subject is positioned. In the photo below, I waited for the exact moment where the trunks of both elephants were clearly visible above the tall grass (where otherwise they would have been lost). In my mind, visual separation can take a photo from being good to great. In fact, when I'm looking through a sequence of images, it's usually one of the main criteria I'm considering when choosing the best image from the bunch!