If you set it to low, you may need to set a higher volateg in the bios.
Say you want 1.3v for your CPU. With low vdroop control, you may have to set the vcore to 1.34 for example within the bios. With higher vdroop control, if you want 1.3v, you would be looking at setting the vcore to asomething like 1.31 or 1.32v.
These numbers are just give you an idea. I just use low vdroop and set a higher voltage in the bios.
By setting the vcore to 1.34 or 1.32 with higher/lower vdroop control, the CPU will still run at 1.3v
(Numbers are just examples and are not based on anything but an example)