You add more pressure, you have to compensate for more fuel. You remove pressure, you don't have to compensate for as much because you aren't getting as much, which is not the best way to use those big injectors. It helps for fine tuning, if anything, but can't make up for the way the SAFC works.

Not a huge range on what you can do with fuel pressure, anyway. Go down to maybe 32, which is pretty damn low, get a poor spray pattern out of injectors. Go up to maybe 50, but only if you're running 20 psi or less, if you want to keep your fuel pump anywhere near the pressure range it can pump enough fuel out.