How can including separate PHP files improve the efficiency and maintainability of a website's codebase?

Including separate PHP files can improve the efficiency and maintainability of a website's codebase by breaking up the code into smaller, more manageable chunks. This allows for easier organization, reusability, and maintenance of the code. Additionally, including separate files can help reduce redundancy and make the code easier to read and understand.

// index.php
<?php
include 'header.php';
include 'content.php';
include 'footer.php';
?>