What is the difference between session_unset() and session_destroy() in PHP, and when should each be used?

session_unset() is used to unset all variables registered to a session, but the session itself remains active. session_destroy() is used to completely destroy the session, including all data associated with it. session_destroy() should be used when you want to completely end a session, while session_unset() should be used when you want to clear the session data but keep the session active.

// Using session_unset()
session_start();
session_unset();
```

```php
// Using session_destroy()
session_start();
session_destroy();