The bios voltage is the no-load applied voltage. When the processor draws a current, the voltage drops. This is normal for voltage supplies, a battery may offer 9.5V in an open circuit but only 8V when connected to a load. When you boot windows, the processor is under slight load so voltage has dropped a bit. This is vdrop. When running prime95, it draws a lot more current and so the voltage drops more, this is vdroop. They're the same effect.
Intel encourages this specification, as voltage decreasing under load makes things less likely to burn out. LLC is defying intel's spec as a result of a few years of overclockers complaining about vdroop. Doesn't matter if they knew what they were talking about or not, you give the customer what they want or they go elsewhere. So now almost all motherboards offer LLC of some sort. Makes people happy being able to set lower numbers in the bios.
I don't much care what my idle voltage is. The processor is not drawing much current at idle, so few electrons are hammering through it and less damage is done. It's under high current conditions that the voltage matters, and llc does nothing to reduce load voltage. All it does is stress the motherboard and give you a happy feeling that your system is safe.
