So far, I've found the stumps very useful for smoothing out and blending lines in my drawings. I also ordered a sandpaper block for cleaning and sharpening the stumps. I use it when switching from blending a dark area to blending a light area and when switching colors in a colored pencil drawing. Both the blending stumps and the sandpaper block can be found here.
I also got a basic set of drawing pencils, which I love! The hardness goes from 6B to 4H, which is just about right for me. The 6B pencil is nice, dark, and soft; the 4H pencil is light, clear, and hard. These Derwent Graphic Pencils really make drawing easier!