Unless we are discussing nitrous engines I believe return style systems as referred to here are not necessary. In a nitrous deal I can see it being used to prevent any aeration in the lines to the nitrous solenoids but also seen many many of those guys who do not bother then either. Those systems are similar to what Crizila described and are to bleed air through small orifice lines at the regulators.
I had my fuel system designed by Magnafuel for a 700 HP blown application. They wanted a -10 return line from the reg. ( -8 to the reg. ) My system is all Magnafuel - filters, fittings, pump, reg.
