In what scenarios is it advisable to use encryption for storing user data in cookies, and what are the potential risks associated with this practice in PHP development?

When storing sensitive user data in cookies, it is advisable to use encryption to protect the information from unauthorized access. This is especially important when dealing with personal information such as passwords or financial details. Without encryption, the data stored in cookies can be easily read by malicious actors, putting user privacy at risk.

```php
// Encrypt user data before storing it in a cookie
$secret_key = "your_secret_key_here";
$data = "sensitive_user_data";

$encrypted_data = openssl_encrypt($data, 'AES-256-CBC', $secret_key, 0, 'your_iv_here');
setcookie('encrypted_data', $encrypted_data, time() + 3600, '/');
```

Make sure to replace "your_secret_key_here" and "your_iv_here" with your own secret key and initialization vector for encryption.