Replacing the global $post object vs. not replacing it.

extras.php

// Template part that DOES replace the global $post object:
?>
	<div class="portfolio-items">

		<?php global $post; ?>

		<?php foreach ( wds_eight_get_portfolio_posts() as $post ) : ?>

			<?php setup_postdata( $post ); ?>

			<div class="portfolio-image">
				<img src="<?php echo get_the_post_thumbnail_url( $post, 'post-thumbnail' ); ?>" alt="<?php echo esc_attr_e( 'Featured Image', 'wds' ); ?>">
			</div>
			<div class="portfolio-details">
				<h2 class="title"><?php the_title( $post ); ?></h2>
				<p class="description"><?php the_content(); ?></p>
				<span class="client-name"><?php echo esc_html( get_post_meta( $post->ID, 'client_name', true ) ); ?></span>
			</div>

		<?php endforeach; ?>

		<?php wp_reset_postdata(); ?>

	</div>
<?php



// Template part that does NOT replace the global $post object:
?>
	<div class="portfolio-items">

		<?php foreach ( wds_eight_get_portfolio_posts() as $post_id ) : ?>

			<div class="portfolio-image">
				<img src="<?php echo get_the_post_thumbnail_url( $post_id, 'post-thumbnail' ); ?>" alt="<?php echo esc_attr_e( 'Featured Image', 'wds' ); ?>">
			</div>
			<div class="portfolio-details">
				<h2 class="title"><?php echo esc_html( get_the_title( $post_id ) ); ?></h2>
				<p class="description"><?php echo esc_html( wds_get_the_content( $post_id ) ); ?></p>
				<span class="client-name"><?php echo esc_html( get_post_meta( $post_id, 'client_name', true ) ); ?></span>
			</div>

		<?php endforeach; ?>

	</div>
<?php


// Helper function for the template part above:

/**
 * Get a post's content.
 *
 * @param  int|string $post_id The post ID.
 * @return string     $content The post's content or empty string on failure.
 */
function wds_get_the_content( $post_id ) {

	$content = get_post_field( 'post_content', $post_id );

	if ( is_wp_error( $content ) ) {
		return '';
	}

	return apply_filters( 'the_content', $content );
}