How can special characters, such as '&' and '=', in URLs affect PHP script functionality?

Special characters like '&' and '=' in URLs can affect PHP script functionality by interfering with the way parameters are passed to the script. To avoid this issue, it is recommended to use the `urlencode()` function to encode special characters in URLs before passing them to the PHP script.

$url = "http://example.com/script.php?param1=" . urlencode($param1) . "&param2=" . urlencode($param2);