sub flattened {
  my( @a, @b ) = @_;
  return @a;  # Returns everything.
}

sub preserved {
  my( $a_aref, $b_aref ) = @_;
  return @$a_aref;  # Returns only the stuff contained in @$a_aref.
}

my @this = qw( 1 2 3 );
my @that = qw( 4 5 6 );

print "$_\n" for flattened( @this, @that ); # prints 1 2 3 4 5 6.
print "$_\n" for preserved( \@this, \@that ); # prints 1 2 3.