What are some potential pitfalls of working with a PHP script that lacks structure and documentation?

Working with a PHP script that lacks structure and documentation can lead to confusion, difficulty in understanding the code, and potential errors when making changes or updates. To address this issue, it is important to refactor the code by organizing it into logical sections, adding comments to explain the purpose of each section, and documenting any functions or classes used in the script.

// Example of refactored PHP script with structure and documentation

// Define a function to calculate the sum of two numbers
function calculateSum($num1, $num2) {
    // Add the two numbers together
    $sum = $num1 + $num2;
    
    // Return the sum
    return $sum;
}

// Call the calculateSum function with two numbers and store the result in a variable
$result = calculateSum(5, 10);

// Output the result
echo "The sum of 5 and 10 is: " . $result;