So. Here goes.
If you've got hardly any money, right, you can only afford to wander to your nearest corner shop, and buy the single packs of loo roll. You know the stuff. Wrapped in a paper packet.
If you can afford to buy two, you'll save some money. Economies of scale, and all that. But the corner shop's still not exactly the cheapest place, although the jolly chap behind the counter has a good stash of magazines he'll let you thumb through, too.
The more money you have, of course, the more loo rolls you can afford to buy in one lump. Drive to the supermarket, and if you don't mind spending a fiver on the things, you get a load of them. Eight, maybe. Maybe sixteen. And because you're buying even more at a time, you save more money.
And if you're really rich, you'll go to the cash and carry, buy an entire box-full of the things, and use them for years. But because you had more money to buy them, you save more money, so you become even richer still.
Now, if I was a university professor, I'd get government funding to explore this kind of thing. But I won't.