That example doesn't show it very well. To be clear: The intended advantage is: Parens are optional. That permits syntax like the following to be implemented in pure Perl without changing the parser:

    try {
        die "foo";
    }
    catch {
        warn "caught error: $_";
    };

If parens were mandatory, it would need look like this:

    try(
        sub {
            die "foo";
        }
        catch(
            sub {
                warn "caught error: $_";
            }
        )
    );

Having the nicer form in the first example is possible only because sigils are mandatory, along with auto-flattening variables and easy code highlighting.

As for the example, with mandatory parens it would look like this:

    w = qq_mult( ConjugateQ, qv_mult( RotationQ, Vector ) );

In production i'd write it like this:

    my $W = qq_mult $ConjugateQ, qv_mult( $RotationQ, $Vector );

That gives a nice balance between a low number of parens, and clarity of intent.