Why I have to call 'exit' after redirection through header('Location..') in PHP?

Question

You know that if you want to redirect an user in PHP you can use the header function:

header(\'Location: http://smowhere.com\');

It is also

Answer 1

If you redirect but you don't die() / exit() the code is always executed and displayed.

Take the following example:

admin.php:

if (authenticationFails)
{
    // redirect and don't die
}

// show admin stuff

If you don't make sure to end the execution after the location header every user will gain access.