Let's say every now and then, you need to do X.

That means you need to be prepared to do X.

And what if some of the components of X expire? That means you have to pay to keep them on hand.

And the distribution of how often you do X is absolutely not predictable. Sometimes it's months between them. Sometimes it's 10 in a day.

If you had to be prepared to serve 20 hamburgers, any given afternoon, with no warning, how much ground beef would you waste, over a year?

Counting how much ground beef you did use does actually provide some information. I'm not discounting that. But it absolutely does not tell the whole story.