So if return; is just as right as return(); , but twice as fast, when would you use return(); ?

In general I wouldn't ;-)

I guess the only two reasons I can think of to prefer return () would be:

• For those people unfamiliar with Perl. In other languages a bare return has often has different semantics (e.g. value of last expression). Making it explicit may help people unfamiliar with Perl. However it would be much better to educate these users rather than code for them IMHO.
• If you were coding a routine that was only being called in list context then it might make sense to use return () just to make it a little more obvious that you were thinking in terms of lists rather than scalars in the code.