The idea is he following: In a old-school normal market, where you sell one good to a whole bunch of guys each etc, and everyone wants just one good, you may just post one price. You will not do better, no matter what you know or do not know.
But in most cases, posting a single price will not be optimal for you. This is because you sell multiple units to multiple customers, each possibly very different. And, you do not know what they would be willing to give you. You have asymmetric information. If you KNEW everything, you could tailor a contract for each customer. But you don't.
In economics, we can tackle this problem using Mechanism Design. Using game theory and nonlinear pricing (the non-linear is important here), you may be able to set a menu of possible contracts in a way that the customer self-identifies by choosing the best option for him.
The intuition of the problem is the following: Choose a menu of contracts that allows you, the company, to maximize profit, while also making the customer choose truthfully and thereby "tell you" what he is willing to pay. This is what the three part price may do for you.
Now why is this not entirely correct? There is a (rather theoretical question) as to basically how far a two-part or three-part price is "nonlinear enough" for your set of customers. This is called implementation theory.
An excellent book to get behind this mystery is Tilman Borgers book on mechanism design http://www-personal.umich.edu/~tborgers/ This was a free download for many years, so you can probably find the pdf.