What are the advantages and disadvantages of creating custom solutions versus using established open-source projects in PHP development?

When deciding between creating custom solutions or using established open-source projects in PHP development, it is essential to consider the advantages and disadvantages of each approach. Creating custom solutions allows for complete control over the codebase and customization to fit specific project requirements. However, it can be time-consuming and costly to develop and maintain custom solutions. On the other hand, using established open-source projects can save time and resources by leveraging existing solutions and community support. However, it may limit flexibility and require adherence to the project's structure and dependencies.

// Example of creating a custom function to calculate the factorial of a number
function factorial($num) {
    if($num == 0) {
        return 1;
    } else {
        return $num * factorial($num - 1);
    }
}

// Example of using an established open-source library for calculating factorial
require_once 'vendor/autoload.php';
use MathPHP\NumberTheory\Factorial;

$factorial = new Factorial();
$result = $factorial->factorial(5);
echo $result;