What is the UX strategy behind Facebook forcing users to use the timeline?

A few months back facebook took the unusual step of forcing most users to switch to the timeline view of their profile page.

I am interested to work out what the strategy was behind this move. On first observation the timeline seems a poor design for readability. However as a presentation method that encourages users to post more pictures/visuals a la Pinterest it makes more sense. Visual posts are shared more than plain text posts... could this have been the strategy behind the policy?

Is their any DATA that shows what behaviours this new layout has promoted? In other words hard data about how it has changed facebook use (not your subjective opinion about whether you like the change!).

Update 15th March 2018: I love reading this question back again. Clearly I can no longer imagine using any other way of looking at my timeline. It has become integral with the way facebook works and also their introduction of historical posts is very clever. People really like those. So kudos to fb ... definitely a good move in my book! (Lisa Tweedie - Original poster)