Whether the math in the first post adds up or not, still it is a good idea to use the options to work faster and reduce energy consumption as a bonus. In winter the system power consumption adds to your room heating. But of course summer is coming and the less heat the better. 

- reduce resolution while experimenting (I vaguely recall there were one-click options to render at 1/2 or 1/4 of dimensions, cannot find them in P13)

- use partial render for just the part you're working on.

- make computation expensive objects such as hair invisible when you are not working on something they have effect on.  

- When working on whole scene (lights, say) use progressive mode so you see right away when the result needs work and cancel the render. Usually there is need to let the render complete in that case. Initial results may be grainy but color/lightness can be seen quite early.  There are  'tiimed 10 seconds' options in render presets.

- switch off DOF and other expensive options while playing around. 

- check your scene lights. Before the days of IBL and environment lighting there were scenes with a huge number of lights to compensate. That does not go well with the way Superfly works. Technology moves forward.

- check your render settings on bucket size and such. See the advice above and in other threads.