Marginal utility per unit consumed is assumed to fall as you consume more.

Does anyone believe in this enough to make use of the concept in business?

Suppose you walk into McDonalds and order a Big Mac.

After the 1st Big Mac you are still hunger and decide to order another one. -- Would you buy a third one? A fourth one?

Suppose that McDonalds recognized that the second Big Mac did not provide you with as much utility as the first one. It decides to make the following offers:

Buy one Big Mac and get a second one for half price.Upgrade your Big Mac to a Super Mac for only another 29 cents.

Would you be more likely to buy the second Big Mac?