Blending can make a drawing look more saturated. It can also help achieve the color/shading you want. Even with the wide range of colored pencils available, there are so many more colors in nature, that it would be impossible for any company to truly make all the colors. One way to achieve the color you want is to layer, then blend the pigments together.
There are many ways to do this.
Word of warning: there are always downsides to any blending method.
The one you choose will depend on the desired results,
the tools you have available and the support and pencils you are using.
Another reason for blending is to eliminate those little tiny white flecks that seem to appear and will not disappear even layer after layer. These are small flecks of the paper showing through the colored pencil.
Because no paper is absolutely smooth, all papers/surfaces will have some texture, some amount of ups and downs. The rougher the paper, the deeper the valleys and higher the hills. The very texture that gives the paper the “tooth” you might want will also be the cause of some of this flecking or other undesired textures.
Part of this can be controlled by making sure your pencil is always sharp and turning it as you draw. Also the length and pressure of the strokes will effect the coverage. Long straight strokes are more likely to be uneven and leave distinct flecking. While you might be tempted to really grind it in, I cannot recommend a heavy pressure. This will result in crushing the fibers of the paper, making permanently indenting the pigment in the paper. Any adjustments will be very difficult. also, it will be really eliminate the flecking. I do recommend a firm but light touch when using this medium, as this will give you the best control.
Note: it will pick up some pigment.
Clean it with a sandpaper pad.
If you press really hard, you will, of course crush the fibers. Sometimes this will actually work to you advantage, and is more effective on thicker paper. I can’t recommend it. I usually do not find it necessary. But I have seen it used very effectively on large dark backgrounds.
Blending pencils can be use throughout the drawing process. It can be used to blend layers together and then more layers can be applied over it. Any wax bloom ( and there usually is) can be buffed away with a soft cloth. There is also a burnishing pencil, a bit harder than the blender and this can be very effective in the end to bring out a shine to the artwork. I usually hold back the burnisher until the work is done, as a finishing touch.
Here I show you a wood block, part of a new drawing of a bird at a bird feeder. The weathered block is wood, but the surface is worn and very smooth.
In this first picture, you can see the color has deepened and the background flecking has been eliminated on the right side of the picture using only the clear blending pencil. On the left the pigments are more uneven and in places the white paper shows though.
In this last photo, the entire platform has been blended with the wax pencil into worn wood. Notice how much richer the colors are, although no new color has been added. Simply a layer of clear wax rubbed in.