Your power bill is a monthly guess
A retailer's bill tells you what the entire house used, once a month, long after you could have done anything about it. It cannot tell you that the second fridge in the garage costs you a hundred and eighty dollars a year, or that the pool pump has been running straight through the most expensive hours of the day.
Clamps on the circuits you care about turn that guess into a live picture, per circuit, in dollars rather than only in kilowatt hours. About half the value of this work is simply finding the always on loads that nobody suspected.