Excellent! I guess this refactoring pattern maps nicely to TheDamian's Always unpack @_ first best practice (PBP, p. 178).

Update: Actually, after thinking about it a bit, it doesn't map exactly. Consider:

my $array_ref = [ qw( 1 4 9 10 15 23 34 84 100 ) ];
add_n_to_values_and_print( $array_ref, 15 );

sub add_n_to_values_and_print{
    my ( $list, $add ) = @_;

    for my $value ( @$list ){
        $value += $add;
        print $value;
    }
}
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This follows Mr. Conway's admonition to unpack @_ but it doesn't accomplish the goal of avoding changes to the reference passed in that Fowler is after. What we really need to do is:

my $array_ref = [ qw( 1 4 9 10 15 23 34 84 100 ) ];
add_n_to_values_and_print( $array_ref, 15 );

sub add_n_to_values_and_print{
    my ( $list, $add ) = @_;

    # dereference and work with a local copy of the array
    my @local_list = @$list;
    for my $value ( @local_list ){
        $value += $add;
        print $value;
    }
}
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Truthfully, that's not a very good example, as I wouldn't generally write code that actually updates the value I would probably write print $value + $add, but for the sake of an example...