<?php
/*
 * Let's say I have defined $settings and I'm storing 
 * a password in $settings['password'] in the file config.inc.php
 */
include('config.inc.php');

// Now I'm using this password in a class
class my_class {
    private $password;
    // and I've defined it as private
    private function __construct() {
        global $settings;
        $password = $settings['password'];
        // Does it make the application more secure, if I unset $settings now?
        unset($settings);
    }
}
?>