Question Why is undervolting laptop GPU while overclocking actually increase the performance?

[Elros]

I try to understand the logic, could someone explain to me this?
If the output is higher than the input must increase as well, no? How come actually resulting in the V can cause better performance?

 

[rgd1101]

under volt mean lower temp.

 

[Phaaze88]

^and lower temp = higher sustained clocks.