Costs that don't include all of the costs are not much use the investor. That's why we don't like EBITDA multiples and, as explained in Lies, Damn Lies and Cash Costs, we don't like 'cash costs' as presented widely in the mining game.
Here's a new one on us, though. What about costs that include negative revenues? Never heard of that one before? Well, neither had we until we started looking at 'cash costs' in more detail.