WordPress post reset query

wp-query-reset.txt

<?php

//https://wordpress.stackexchange.com/questions/144343/wp-reset-postdata-or-wp-reset-query-after-a-custom-loop

The difference between the two is that

-> wp_reset_query() - ensure that the main query has been reset to the original main query
-> wp_reset_postdata() - ensures that the global $post has been restored to the current post in the main query.

wp_reset_query() calls wp_reset_postdata(). The only difference between the two then is this line:

$GLOBALS['wp_query'] = $GLOBALS['wp_the_query'];
(in wp_reset_query()). So wp_reset_query() is only necessary should those two globals differ, and that only happens if query_posts() has been used somewhere.

When should I use them?
Simply put:

wp_reset_postdata() - immediately after every custom WP_Query()
wp_reset_query() - immediately after every loop using query_posts()