Today's generation is hooked to Facebook 24x7! Constant notifications for comments, status updates, photographs etc. force you to stay connected to the internet almost all the time. But, there is no guarantee of a regular supply of 3G/2G data no matter how good the service may be. As a result, you may miss out on some action in between!
But Facebook is smart and understands your needs. Hence, it boasts a feature wherein you can receive important notifications via SMS.