The new data reports on the percentage of fans that saw your post through normal means, and those reached through a promotion. Additionally, you’re also able to view how many unique people viewed it, both organically and virally — which Facebook defines as the number of people who saw your Page in a story from a friend.
You’ll also notice a Promote button that appears to the right of the data. If you’re interested in expanding your reach, you can set your budget (how much you’re willing to spend) and Facebook will tell you what you’re estimated reach will be.
Considering Pages reach only 16 percent of fans, this is a smart move by Facebook. By displaying reach details on Timeline instead of Insights, the company is able to gently nudge Page owners to consider investing in Sponsored Stories or Reach Generator — a premium offering guaranteeing that a Page reaches at least 75 percent of fans within a month.
Currently it’s unclear how many Pages have access to this data or when Facebook plans to roll it out to all Pages.