Utility Bills HELP

[PlyrJames791]

I was hoping to create an object that can report a family's utility usage, after seeing the "Utility Bill - Energy" and "Utility Bill - Water" globals in the expression primitive's attribute picker. I've made the object, and the cost does appear to increase when I leave the lights on or a sim takes a bath. I'd assumed that these two values would contribute to the bills that are delivered by the mailman, but I've just read somewhere that the bills are actually based entirely on the value of the lot, and not the utilities used. So my question is, do the utilities actually affect the bills or not? And if not, what are they for?

Thanks :)