how neccesary is a return line for a electric fuel pump?

When I was a 20 something around 1979 I had a Cadillac EFI pump supplying the 440-6 in my 69 Dart. I made an adjustable return out of a brass "T" with spring and check ball that dumped back into the filler neck. The pop off was at about 20 pounds or so and then the big Holley regulator cut it back to 7 at the engine. This was able to supply enough fuel through 5/16 line to run high 12s at 4000' ASL. If you tried to dead head that pump it would literally blow up the rubber fuel line segments.