wpdb->prepare delete example confusion

Hi,

I am a little confused with the delete example here

http://codex.wordpress.org/wpdb_Class#Examples

It says

$wpdb->prepare(
		"DELETE FROM $wpdb->postmeta
		 WHERE post_id = '13'
		AND meta_key = 'gargle'
		"
	,$id, $key )

I was wondering whether it’s better to be something like:

$id = 13;
$key = "gargle";
$wpdb->prepare(
		"DELETE FROM $wpdb->postmeta
		 WHERE post_id = %d
		AND meta_key = %s
		"
	,$id, $key )

Actually my question is, if i need to use variables (like $id, $key) i should use %d/%s for placeholders in the query and then put the variables as following parameters in the prepare function right ?