Using a private taxonomy can give huge performance gains. I'm going to cover some examples of the things you can do, and the gains to be had.

Setting Up Your Utility Taxonomy

We'll be using this taxonomy to mark posts, but since it won't be public facing, the registration code is quite small:

function tomjn_utility_taxonomy() {
	$args = array(
		'label'		=> __( 'Internal Markers', 'tomjn' ),
		'public'	=> false,
		'rewrite'	=> false,
	);
	register_taxonomy( 'utility', 'post', $args );
}
add_action( 'init', 'tomjn_utility_taxonomy', 0 );

We can now search for posts very quickly by tagging and flagging posts. A lot of developers will use post meta to store this kind of information, but this leads to super expensive post meta queries.

But that's not all that we can do.

Filtering Things Out On Homepages

We're going to use this to make filtering and excluding posts on the homepage obscenely fast. Most users will save a post meta field named hide_from_home but this is the worst way imaginable to do this for performance. The meta query to filter those posts out can add seconds to your loading time. With enough visitors it can bring down a database server. Adding more posts to your site makes these queries even more expensive, and in a non-linear fashion.

Instead, we want to query for what we actually want, so why not mark all posts with show_on_homepage on publish? Then we can remove that tag for posts we want to exclude without incurring a performance cost. We can even tag them with a hide_on_homepage tag so that they can be listed

Automated Post Marking, & The Home Page

So lets automate this. Starting with the publish_post hook:

function tomjn_auto_add_to_home( $post_id ) {
	wp_set_object_terms( $post_id, 'show_on_homepage', 'utility', true );
}
add_action( 'publish_post', 'tomjn_auto_add_to_home' );

Now all posts are set to show on the homepage when published, and we can adjust the homepage query to only show these posts with pre_get_posts:

function tomjn_only_show_home( $query ) {
	if ( $query->is_home() && $query->is_main_query() ) {
		$query->set( 'utility', 'show_on_homepage' );
	}
}
add_action( 'pre_get_posts', 'tomjn_only_show_home' );

Now all that needs to be done to hide a post from the homepage is to uncheck show_on_homepage in the edit screen. Other tags can be added for hiding from other areas, or even promoting posts

HomePage Carousels and Feature Sections

Some developers will store an option with a list of post IDs of what to show in the carousels on pages. They might even try to exclude posts from featured areas But this is inflexible!

What if editorial wants complete control of what posts appear in a highlight reel? What if we want more than 1 carousel!

Well, why not use a taxonomy? With a hidden featured_area taxonomy we can group posts together into featured areas, such as homepage_gallery, or food_section_highlights.

Now, whenever you want a post to show in a featured posts section, tag it accordingly.

We can even swap areas and galleries out by storing the term to display in an option, rather than the posts.