Help me understand a bypass regulator location

Having a extensive knowledge on hydraulics, (33 years a firefighter,19 years a driver engineer), how can placing a pressure regulator after the carburetor, limit the pressure a carb. sees?
If you look at the diagrams on the Holley PDF, if you look at figure 3 how is this set up going to limit the amount of pressure the carb. sees? I mean in figure2 I can see "how it works."


[ame]http://documents.holley.com/199r7914-3rev6.pdf[/ame]