I agree . We're in 4.0 .
First, Work is the first reason .If u have some problem with ur homework , we will find solution in social networking site.
Second , It's a party , date ,etc . Do u think we meet to ask them a party day in real life ? Why dont we do it in NetWork , Blog , Messenger ?
Finally , It's ur social life. You can play a game , post a video , call video , chat with them . It's make ur active , friendship , etc .