在下面的示例中（从WordPress.org）获取提要后，为什么要删除过滤器

<?php
function return_7200( $seconds )
{
  // change the default feed cache recreation period to 2 hours
  return 7200;
}

add_filter( \'wp_feed_cache_transient_lifetime\' , \'return_7200\' );
$feed = fetch_feed( $feed_url );
remove_filter( \'wp_feed_cache_transient_lifetime\' , \'return_7200\' );
?>