Why is better to use filter_input()?

Question

This should be a elementary question but why is better to use something like this:

$pwd = filter_input(INPUT_POST, 'pwd');

Instead of just:

$pwd = $_POST['pwd'];

PS: I understand that the filter extension can be used with more arguments to provide an additional level of sanitization.

Answer 1

Any data which is sent from the client (such as POST data) should be sanitized and escaped (and even better, sanity-checked) to ensure that it isn't going to kill your website.

SQL Injection and Cross-site scripting are the two largest threats for failing to sanitize your user-sent data.

Answer 2

It's not. $_GET, $_POST, $_COOKIE and $_REQUEST are filtered with default filter. filter_input(INPUT_POST, 'pwd') without additional parameters also uses the default filter. So there is no difference at all.