Think about what the SAFC does. It adds or takes away fuel where the stock ECU is unable to. Really depends on the mod level of the car. If your car is modded enough that the ECU has a hard time 'deciding' how much fuel to give the car, then an SAFC will be useful to give the car ideal conditions. For example, if you have a cold air intake, you're gaining about as much power as moving to New York. The ECU can adjust to this. You really won't need to start adjusting your fuel values until you get big upgrades, like forced induction, or cams, ported head, etc.