A good example is Facebook Custom Audiences. Within this Facebook supports email targeting, the ability to upload customer email addresses and then target those users on Facebook with tailored ads. This lets you micro-segment based on your existing customer database. One application is customer loyalty marketing, promoting offers to existing high value users via Facebook ads.
You can also use organic to increase audience engagement with your content. For example, let’s say you’re a ticketing website for sporting events and you know that some of your followers are rugby fanatics. If you have a new blog interviewing Dylan Hartley (current England captain), then it makes sense to personally contact them (or at least key influencers) via their preferred social network and tell them about the blog, and ask them to comment/share. It’s personal and increases the chance they’ll see/read your content.
Now, it is not that these sites are not interested in Google users. In fact, they have hired us to help them increase their share. However, they are getting so much traffic from sites like Facebook that it seems there is less urgency about attracting this traffic and less willingness to change the site to meet organic standards. Not long ago, sites would urgently and unquestioningly abide by Google’s standards to court that traffic.