What performance and caching considerations become especially important when developing a WordPress plugin that will run on a high traffic website?

A WordPress plugin running on a high traffic website needs particular attention paid to performance, since a poorly optimized plugin, such as one that runs an expensive, unnecessary database query on every single page load regardless of whether that specific page actually needs that data, can noticeably slow down an entire site, and important considerations include using the WordPress Transients API or an external caching layer like Redis to cache the results of expensive operations, being careful about exactly when and how often a plugin's hooked functions actually execute, and avoiding loading unnecessary CSS or JavaScript files on pages where a plugin's specific functionality is not actually being used at all.

$data = get_transient('expensive_report_data');
if ($data === false) {
    $data = generate_expensive_report();
    set_transient('expensive_report_data', $data, HOUR_IN_SECONDS);
}