Why does the user need to unset variables like $topic_subject, $last_thread, and $last_author at the end of the script, and what purpose does it serve?

When variables like $topic_subject, $last_thread, and $last_author are unset at the end of the script, it helps to free up memory that was allocated to these variables during the script execution. This is important for optimizing memory usage and preventing potential memory leaks in the PHP script.

// Code snippet to unset variables at the end of the script
// Some code here...

unset($topic_subject);
unset($last_thread);
unset($last_author);