The first is increasing **Engagement** particularly with richer content.

Here are some studies I found that point to whether this worked. It's a mixed bag.

This one shows mixed results for engagement and pageviews: [Attention USA][1]

And this from Mashable: [Fan growth slowed after timeline introduced][2] ... but did it pick up again after people got used to it?

This study suggests some positive impact for marketers - [Simplymeasured.com][3]

> 1. 14% Increase in Fan Engagement
2. 46% Increase in Content Engagement
3. 65% Increase in Interactive Content Engagement (Video and Photo)

This study suggests little impact: [allfacebook.com][4]

However here is a rebuttal: [jonloomer.com][5]
(Basically proposing that timeline could impact on the things that matter - more visits and more engagement with apps)

I can't locate it now, however I recall seeing another report that found a decrease in interaction with wall posts (of the user's friends) via timeline. However this is far harder to find as the emphasis has been on marketing impact for logical reasons. 

Bottom line: *The results seem positive but there isn't a strong consensus yet*


The second reason is **Encouraging a different level of sharing**

From a [FastCompany article][6] interviewing Timeline's designer:

> Wanted to convey feeling...The feeling of telling someone your life story, and the feeling of memory--of remembering your own life....

Also from one of the designers (Nick Felton, who is famous for infographics)

> Time is the most universal framework across cultures... It’s a shell on which users themselves can define what they want to highlight.

and finally:

> Facebook wanted the Timeline to be a place for self-expression: A way for users to reveal who they are and what their lives are about.

More sharing supports the reason for Facebook's being.


  [1]: http://www.attentionusa.com/2012/06/study-has-timeline-been-a-boon-or-bust-for-brands/
  [2]: http://mashable.com/2012/04/20/fan-growth-slowed-facebook-timeline/
  [3]: http://allfacebook.com/study-facebook-timeline-doesnt-affect-engagement_b84257
  [4]: http://allfacebook.com/study-facebook-timeline-doesnt-affect-engagement_b84257
  [5]: http://www.jonloomer.com/2012/04/02/impact-of-facebook-timeline-on-news-feed-engagement-meh/
  [6]: http://www.fastcodesign.com/1665414/designers-behind-facebook-timeline-5-keys-to-creating-a-ui-with-soul