Did you look at the link? LLC forces a steady voltage regardless of load, attempting to emulate a perfect voltage source. However it does not have a perfect voltage source available, so when the load changes, the voltage stays 'constant' but rings around the mean value.
The voltage set in the bios is never meant to be a 'target' voltage, it's the voltage intended when completely idle. When drawing more current, the voltage across the processor decreases much like any other circuit component. Intel expect and design for this. By enabling llc you are forcing the voltage to run out of intels spec for the comfort of being able to type in a lower number, the penalty is that the ringing drives far higher voltages through the chip when transitioning from idle to load. I believe you can even watch the voltage doing this using everest, the resolution is sufficient to guess at how high the voltage spikes.
If you were really keen, I believe fourier analysis would allow you to model this. If you'd rather put your fingers in your ears and sing loudly, happy in the knowledge that you've set a lower number in the bios, then do so.
As a more intuitive way of looking at it, in case the graphs are not immediately obvious by themselves. Heat and low voltage combined kill processors, either by itself doesn't matter much. So with llc disabled, you get a higher voltage when idle. However with it enabled or disabled, you need the same voltage under load to maintain stabilty.
So all llc permits is a lower idle voltage, which is when the chip is cool and the voltage doesn't matter anyway. The penalty is driving large transient voltages through the chip, and presumably working the motherboard power circuitry a lot harder. The former is dangerous, the latter surely hurts stabilty rather than helps.
