All of Wacom's tablets are pressure sensitive-- they literally feel the full range of pressure from the pen on the tablet. With a pressure-sensitive tool, such as Photoshop's Rubber Stamp or History brush or any Painter brush, you get unparalleled control. Press hard, and you get a more opaque clone, a fatter paintbrush, a darker stroke.
Press lighter, and you have a transparent clone, a thin brush, a gentle stroke of color. It's intuitive, because it's how tools work in the real world. If you spend any time at all creating and working with images on a computer, a pen tablet will make you faster. You can go from light to dark, thin to thick, or opaque to transparent in one pressure-sensitive stroke. The pen's absolute positioning is also faster than a mouse, allowing you to access every area of your screen without detours.
