What are the advantages and disadvantages of using HTML attributes like "required" versus custom PHP validation for form handling?

When handling form validation, using HTML attributes like "required" can provide client-side validation for users, giving them immediate feedback on missing or incorrect data. However, relying solely on HTML attributes for validation can be bypassed by users who disable JavaScript or manipulate the form submission. Custom PHP validation provides server-side validation, ensuring data integrity and security, but requires additional coding and may not provide instant feedback to users.

// Custom PHP validation for form handling
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $name = $_POST["name"];
    $email = $_POST["email"];
    
    if (empty($name) || empty($email)) {
        echo "Please fill in all required fields.";
    } else {
        // Process form data
    }
}