Overclocking Video Card, Core/Shader

http://www.legionhardware.com/document.php?id=687&p=7

According to this, the shader clock doesn't really matter, is that true? Those games tested are a bit old.

Also, since you can unlink the clocks now, why was there a specified ratio in the first place? Like now you still can choose to link them, what was the point of linking them in the first place if you can unlink them? Is there some special benefit to keep the shader/core at a certain ratio?

A slightly different topic, is it very dangerous to overclock the vram?

Thank you.