WP_Query::reset_postdata() sets the global post variable ($GLOBALS[‘post’] === $post) to the current post in the loop of the current WP_Query instance. public function reset_postdata() { if ( ! empty( $this->post ) ) { $GLOBALS[‘post’] = $this->post; $this->setup_postdata( $this->post ); } } What that means is that, if you run a custom query on a page, … Read more
No. get_posts() does not modify global $wp_query variable and it doesn’t need to be cleaned up. Note that if you further use setup_postdata() you do need to wp_reset_postdata() afterwards.
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. Indeed, looking at the source you’ll see that the wp_reset_query() calls wp_reset_postdata(). The only difference … Read more