"Reduce the cost of your energy bills" said the spam.
But actually, you can. It was quite a while ago that I did this. I opted to get my bills via the internet, rather than on paper. Obviously, this is cheaper for the company doing the billing, and by doing this, I avoided a charge of £2 per quarter. Or to put it another way, the cost of my energy bills went from £8 to zero!
I don't think that's what the spam meant, but it's a nice way to make a small reduction in your expenditures.