Paraphrasing Piers Cawley talking about why to give up Ruby for Perl (paraphrased):

This is assembly language for calling a function:

push address of RETURN on stack push $argument on stack get address of FUNC goto FUNC RETURN: pop return value off of stack

This is Perl 5 for calling a function:

func($argument);

That's all well and good. This is assembly language for entering a function:

pop parameter from stack verify parameter type constraints ...

This is Perl 5 for entering a function:

sub func { my $parameter = shift; die 'Wrong type' unless $parameter->isa( 'Whatever' ); ... }

... but wouldn't it be nice if:

sub func(Whatever $parameter) { ... }

(No new insight here, but directly prior to this talk, Damian Conway and I talked about how Perl 6 signatures simplify much, much more code than this simple example illustrates. Lots of code goes away.