Fuel lines - why have 2 ?

So I have have 4 A body’s and none of the slant cars have had a return fuel line but my 318 cars have .

I have a 318 challenger too and wondering if it’s really a must for have the return line or not . I get why it’s there . But is it a must ? Because many cars in late 60s early 70s didn’t have one either .

I just don’t want to run a second line if I don’t have too.