The main benefit of return vs returnless is the fuel pressure response is faster on the return setup. You can adjust the fuel pressure via the PCM, but in certain scenarios, the response to sudden throttle changes is quicker if it's all manual.

2000 Rio Red I4 Cougar 200whp & 210wtq at 9psi 254whp & 276wtq with NX 35shot WRX TD04 Turbo, Cut Short Shifter, Strut Tower Bar, 17" ZN Wheels, Roush Springs, Starion Intercooler, NX 35 shot, HKS SS BOV, Full 3" exhaust,StreetFlight Chip