How can the use of internal functions versus external PHP files affect the overall structure and functionality of a PHP script?

Using internal functions within a PHP script can make the code more organized and easier to maintain, as the functions are contained within the script itself. On the other hand, using external PHP files for functions can modularize the code and make it more reusable across multiple scripts. The choice between internal functions and external files depends on the specific requirements of the project and the developer's preference.

// Example of using internal functions within a PHP script
function calculateSum($a, $b) {
    return $a + $b;
}

$result = calculateSum(5, 3);
echo $result;