Are you sure your website would be back up and running in a few hours after a catastrophe happens? If you use a MySQL database to store user information and other website information, you need to have backups of your database in case of a failure...
By using PHP includes in your PHP scripts you can greatly increase your productivity. By using PHP includes, you can also make template files, and make updating your website incredibly easy.
PHP is one of the most used scripting languages on the internet today. You don’t need to know a lot about PHP to create a PHP file. A PHP file is much like an HTML file with a few differences.