People with kids usually post a significant amount of anecdotes, observations and photos about their kids. I can totally see that people could pay to get these backed up, formatted nicely and provided as a separate web service, a slideshow or a physical book that they could give to their kids later.
The thoughts I posted to Facebook, and the tweets I tweeted were fairly low-value content. I deactivated my FB account and stopped tweeting from my personal twitter account; if I never saw those tweets or status updates again I don't think I'd be worse off.