Why use Ubershaders?

[Silent Hell]

So I know the question may sound retarded, but there's something I've been wondering for a while. As I understand it, Shader Compilation causes stuttering during gameplay, so once the shaders have been compiled, they are stored in the Shader Cache until next time to avoid this problem. So then, what is the point of ubershaders when there is an option to compile the shaders before the game starts? If all the shaders are compiled then would there not be a reason to use ubershaders? Or do they just guess what shaders will be needed and not actually compile them all?