Kill switch, if your X-VPN is disconnected unexpectedly, it will automatically disconnect your network connection to avoid your data leaking.
You will get better privacy protection by turning on "Kill Switch". There are two situations that which X-VPN may get disconnected. Your X-VPN account password is changed when you are connected to premium servers. Or X-VPN may disconnect accidentally due to the network fluctuations.
You may turn on Kill Switch from "Advanced Features".