It idles at under 4 watts. So what is the benefit of undervolting it? It undervolts and underclocks itself, automatically.
In either case (undervolted or not undervolted) it will ramp up if you put a load on it and in any realistic situation that load won't tax it even 50%. In either circumstance it will use the same wattage... just enough to process the load... then return to idle. Right?
So many flaws in your reasoning. Maybe some of us have usage patterns that don't fit the parameters of what you just described?
I run mine flat out, 400% load 24/7. Protein folding simulation for the SPCR F@H team. Moreover, this being SPCR and not HotHardware or HardOCP, I have an obsession with silence. I want to ensure that load temps don't exceed 45C* under ANY load for ANY period of time, and I want to do so while avoiding any cooling solution that would compromise the peace and quiet of my den.
(*achievable at stock frequency by undervolting. In reality my target max temp is 55C but I run at 4 GHz)
Also please realize that wattage (electrical power consumed) and processing power are not correlated. I could run my CPU at 3 GHz@1.0 volts or at 3 GHz@1.5 volts. 'Processing the load' will take exactly the same amount of time in both scenarios. One consumes 50% more power to do so.
The idea is to run the hardware as efficiently as possible by finding the minimum stable voltage at any given clock frequency. That's what we do when overclocking; when we do it at stock frequency we just call it a different name, "undervolting".
Moreover, 'minimum stable voltage' vs. 'clock frequency' is not linear. It is typically an exponential curve. Clock frequency vs. processing time is (ideally) linear. Therefore, given a CPU always running at minimum stable voltage, you will use more power for a given load the faster you try to complete it.
Basically you are wrong on about 3 levels.