Example of Use cases for Actions

functions.php

<?php

/**
 * code #1 - removes excess Wordpress header tags from default themes.
 */
function clean_wp_header() {
  remove_action('wp_head', 'wp_generator');
  remove_action('wp_head', 'rel_canonical');
  remove_action('wp_head', 'rsd_link');
  remove_action('wp_head', 'feed_links',2);
  remove_action('wp_head', 'feed_links_extra',3);
  remove_action('wp_head', 'wlwmanifest_link');
  remove_action('wp_head', 'wp_shortlink_wp_head', 10, 0);
  remove_action('wp_head', 'adjacent_posts_rel_link_wp_head', 10, 0);
}
add_action('init', 'clean_wp_header');




/**
 * code #2 - display Wordpress database query times and memory consumption in footer
 */
function footer_stats_display($visible = false) {
  $stat = sprintf( '%d queries in %.3f seconds, using %.2fMB memory',
    get_num_queries(),
    timer_stop( 0, 3 ),
    memory_get_peak_usage() / 1024 / 1024);
 
  echo $visible ? $stat : "&gt;!-- {$stat} -->" ;
}
add_action('wp_footer', 'footer_stats_display', 20);


/**
 * code #3 - output the current post/page template name in your header area
 */
function display_template_name() {
  global $template;
  print_r($template);
}
add_action('wp_head', 'display_template_name');



/**
 * code #4 - Change Login Page Logo, URL and title tag
 */
 function custom_login_logo() {
 echo '<style type="text/css">h1 a { background: url('.get_bloginfo('template_directory').'/companylogo.png) 50% 50% no-repeat !important; }</style>';
 }
 add_action('login_head', 'custom_login_logo');

function change_wp_login_url() {
	return bloginfo('url');
}
add_filter('login_headerurl', 'change_wp_login_url');

unction change_wp_login_title() {
	return get_option('blogname');
}
add_filter('login_headertitle', 'change_wp_login_title');



/**
 * code #5 - Redirect To Post If Search Results Return One Post
 */
add_action('template_redirect', 'redirect_single_post');
function redirect_single_post() {
    if (is_search()) {
        global $wp_query;
        if ($wp_query->post_count == 1 && $wp_query->max_num_pages == 1) {
            wp_redirect( get_permalink( $wp_query->posts['0']->ID ) );
            exit;
        }
    }
}


/**
 * code #6 - Change user base rewrite url from "/author/name" to "/profile/name"
 */
add_action('init', 'cng_author_base');
function cng_author_base() {
    global $wp_rewrite;
    $author_slug = 'profile'; // change slug name
    $wp_rewrite->author_base = $author_slug;
}

Thanks but I notice if child theme this will not work

 echo '<style type="text/css">h1 a { background: url('.get_bloginfo('template_directory').'/companylogo.png) 50% 50% no-repeat !important; }</style>';

here are my update

   // check if child theme
        $path = get_template_directory() === get_stylesheet_directory() ? get_bloginfo('template_directory') : get_stylesheet_directory_uri();
        echo '<style type="text/css">h1 a { background: url(' . $path . '/companylogo.png) 50% 50% no-repeat !important; }</style>';

Nice. Thank you.

We can also use this function
get_theme_file_uri('/companylogo.png')
https://developer.wordpress.org/reference/functions/get_theme_file_uri/