Not much, unless you've done fuel-related mods like larger injectors. Technically, if you increase fuel pressure, you also increase the amount of fuel going through the injector, but that only stands true to a certain point. You can only push so much fluid through an orifice, no matter how much more pressure you apply to it.
Having an adjustable regulator, in my case, will give me the ABILITY to increase fuel pressure if I need to. Since my injectors are so much bigger, every time one fires it causes a slight drop in fuel pressure, which is only replaced by more flow from the pump. Having increased pressure in the rail reduces the drop in pressure, keeping relatively more stable rail pressure, therefore the injectors will fire more evenly.
When it comes to fuel delivery, you want everything to work the same at each cylinder, so you have an even power distribution across all cylinders. Having a gauge and an adjustable regulator are just a couple of things that will help you to have control over this.
I should open a performance engines school.
