Reasons behind wanting a low-power HTPC

I've seen a few post recently where the question was asked: "What parts would give me the lowest power HTPC?".

So my question is this: Why?

A - Are you looking to "lower your carbon footprint"? (btw,..I typed that with a lot of sarcasm!!! My keyboard is a mess)
B - Are you looking to lower your electricity bill? (admirable, but I doubt you'll save as much as you hoped you would)
C - A combination of the first two?
D - Something else entirely?