Upping the contrast produces lighter lights, darker darks, and a wider range of tones in between—making your image look just a little better than what you’d see in real life. On the other hand, reducing contrast can give an image a more flat, even tone. As with saturation, too much contrast is usually not a good thing.
The contrast on your art journal pages, they'll be bolder, more vivid, and definitely more dramatic. This principle of art can help you achieve more interest and make your pages pop. With contrast, you can intensify the mood!