How can including specific parts of PHP code in different files affect code maintenance and readability?

Including specific parts of PHP code in different files can lead to code duplication, making maintenance more difficult and increasing the chances of errors. To improve code maintenance and readability, it is recommended to use include or require statements to import common code snippets into different files, reducing duplication and ensuring consistency across the project.

// common_code.php
<?php
// Common code snippet
function commonFunction() {
    // Function logic
}
?>

// file1.php
<?php
require_once 'common_code.php';
// Code specific to file1
commonFunction();
?>

// file2.php
<?php
require_once 'common_code.php';
// Code specific to file2
commonFunction();
?>