I'll explain it very simple.
Not every processor/graphic chip is of the same "quality". That's why a manufacturer sets the voltage at a certain level where there is the best balance between battery performance/producing cost.
But this also means that if you are lucky you get a "good chip", where you can set the voltage lower. This is called "undervolting".
With the Surface Pro 3, you can do that with the program Intel XTU.
Now what we also need to know is that lower voltage doesn't mean the performance is worse.
Yes higher processor clock does need more voltage (or let's say "power consumption"), but if you set an voltage offset lower, it doesn't affect performance, unless the voltage is too low for the processor to handle and the system gets unstable.
The reason why you want to undervolt are obvious:
- longer battery life (because of reduced power consumption)
- less heat (less power consumption -> less heat production)
But again. You can't undervolt every chip and if you can, not every chip can be undervolted the same.
If you want to know a little more about the Surface Pro 3 undervolting, take a look here:
http://www.gamerheadlines.com/2014/...oost-performance-by-20-reduce-heat-and-noise/
Hope I helped you a little bit.