just to increase fuel supply for ur injector.. but its become useful IF only u have piggyback (eg E-Manage) or stand alone ECU to program better timing sequence..
as last time i only did change management using chip inside ECU, i never use fuel regulator.. usually people who use fuel regulator already change to mild cam or full race cam where its fuel supply need to increase by a lot n its injector already change to bigger cc n fuel pressure will definitely being use..