IOH voltage and CF

Have done alot of reading about this and can't find any "real" answers.
Some claims that it is necessary to increase it when running at CF, others doesn't even know what it is.

Take this for an example

IOH is easy, if you are running a single PCIe card (graphics card), give the IOH 1.3V, if you are running more than one PCIe graphics card, give it 1.35V.

Click to expand...

I have no idea, but i have two option in my bios. IOH voltatge and IOH PCIE voltage.
So does the claims have some truth in it or is it bogus.

Bump