[WordPress] An second, more general example of how using a variable even if it's only to be used once can improve the readability of code.

passing-variables-in-wordpress-for-loop-basic.php

<?php

// The basic `for` loop
for ( $i = 0; $i < 10; $i++ ) {
  // Do iterative work
}

passing-variables-in-wordpress-for-loop-optimal.php

<?php

/* The basic `for` loop with the length of the collection
 * being stored once so it isn't checked every time
 * the loop runs.
 */
for ( $i = 0, $l = 10; $i < $l; $i++ ) {
  // Do iterative work
}

/* A second example as to how storing the size
 * of the results can result in a more performant
 * loop.
 *
 * Assume the arguments for retrieving posts have
 * already been defined.
 */
$args = array(
	'post_type' => 'acme_post_type',
	'tax_query' => array(
		'relation' => 'AND',
		array(
			'taxonomy' => 'acme_labels'
			'field'    => 'term_id',
			'terms'    => 100
		),
		array(
			'taxonomy' => 'acme_labels',
			'field'    => 'term_id',
			'terms'    => 200
		)
	)
);
$posts = get_posts( $args );

$post_count = count( $posts );
for ( $i = 0; $i < $post_count; $i++ ) {
  // Do iterative work
} 

passing-variables-in-wordpress-foreach-loop.php

<?php

/* A second example as to how storing the size
 * of the results can result in a more performant
 * loop.
 *
 * Assume the arguments for retrieving posts have
 * already been defined.
 */
$args = array(
	'post_type' => 'acme_post_type',
	'tax_query' => array(
		'relation' => 'AND',
		array(
			'taxonomy' => 'acme_labels'
			'field'    => 'term_id',
			'terms'    => 100
		),
		array(
			'taxonomy' => 'acme_labels',
			'field'    => 'term_id',
			'terms'    => 200
		)
	)
);
$posts = get_posts( $args );

foreach ( $posts as $post ) {
  // Do iterative work
}