In this case i wanted to have mountains with "higher" slopes but also some plain areas and of course a smooth beach.
The idea behind the blending is to control the roughness of the different areas. If you use the same noise seed as blendshader, you will have the rough mountains and smooth plains.
Also you get an "overall slope" thats not linear but kind of a square function.
Some Images to explain:
This is what the first fractal would look like w/o blending:
And this with blending it with the same noise:
The same is for the smaller fractal. without blending:
You get decent slopes and roughness in the plain areas while having nice rough mountains.
I think you can get the same think with a few distribution shaders, but imho this is easier.
Also you can control offset, roughness of the initial noise etc to get very different results.