The basic purpose of a FPR is to maintain a constant pressure across the fuel injector. As you open and close the throttle, the pressure in the intake manifold varies greatly from relatively high vacuum (low pressure) at idle to pretty low vacuum (high pressure, almost atmospheric) at wide open throttle. For the injectors to function correctly, there needs to be a constant pressure difference between either side (one side exposed to the manifold vacuum, and the other exposed to the pressuized fuel system). So when intake manifold vacuum increases, fuel pressure must drop accordingly or the injectors will be over-pressuized, or visa versa. The function of the fuel pressure regulator is to adjust the fuel pressure to correspond to the intake manifold pressure.

As with any other component of the fuel system, there is absolutely NO benefit in messing with it on a stock application. There generally is little reason to mess with it at all on NA applications. Forced induction is a different story, however. Force-fed engines actually experience POSITIVE intake manifold pressure (negative vacuum). This means fuel pressure has to rise significantly in order to maintain injector pressure. In this case, you need a FPR that can handle much greater fuel pressures than the stock unit can (in addition to a fuel pump that can PROVIDE that increased pressure in the first place).

Hope that helps.