If you want to use WhatsApp without showing all your actions, then this option is only for you. People will think that you are offline, but it will be vice versa. By enabling this option, you can use whatsapp secretly without any visibility of being online and without showing blue ticks
FM WhatsApp You’ll obtain each message sent by anybody. Only one tick will be visible to the sender. You can watch statuses secretly, and your WhatsApp last seen will be frozen.