Social Networks

I have read a lot about the need to make use the various social networks and yet I haven't been able to see the need. I have setup a facebook page and a live journal. I setup the live journal page because the face book just wasn't pretty. so, now I have a blog, a main web page, a facebook and a livejournal page to promote Wade-In Publishing, oh and not to mention the twitter. Did you know you can set the twitter to update every time you make a post on any of the social networks? Great idea, but a little wasted. I'm not getting it. Do you realize how much posting it would take so each site doesn't share all of  the same information? I visited a couple of author's sites and basically the same thing is posted on each.  I was a little bored with the visit. So what is the point?