It doesn't. Pspd, or pitch speed, is the theoretical maximum speed the airplane can fly at, assuming zero drag and perfect conditions, i.e. the propeller is screwing through the air like a bolt through a nut, dragging the plane behind it...

The drag of the airplane is what determines the in-flight airspeed.

Of course it is possible for an airplane to exceed the propeller's pitch speed, because the prop blades are actually airfoils, and create lift. If the lift force generated by the prop exceeds drag, the airplane will accelerate. The faster the airplane goes, the more drag is generated airframe, and the less lift is generated by the prop. Eventually you reach equilibrium, where the plane is going flat out at its maximum speed.