As opposed to what? arrays and hashes? You can't pass those to subroutines. You can only pass a list of scalars to a subroutine. If you have an array or a hash in your parameter list, it gets flattened into a list of its elements. Sometimes, one can recreate the array or hash from that list. But while the whole concept of flattening an array or a hash then creating a new array or hash is pretty icky, the real problem is that often one cannot recreate the original variables.

sub f {
    my (@a,%h) = @_;
    print("The array has ", 0+@a, " elements\n");
    print("The hash has ", 0+keys(%h), " elements\n");
}

my @a = qw( a b c );
my %h = ( d=>4, e=>5, f=>6 );
f(@a,%h); # Same as f($a[0],$a[1],$a[2],'e',$h{e},'d',$h{d},'f',$h{f})
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The array has 9 elements
The hash has 0 elements
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Since one often has to use references, it's not a bad idea to default to passing a reference. At least, that's the reason I do it. It gets confusing if you're not consistent.