Facebook insights is a how brands, groups or opinion leaders can track their reach, the demographics of who "likes" them and how people are interacting on the page. The data I provided is for The University of Minnesota CLA Student Ambassador.
For brands it is a way to evaluate how the brand is being perceived, and if public are aware of it. Facebook has 1 billion users, so it tends to be a good indicator of the publics. Insights also provides a way to see how page admins should utilize the page. For brands like target, many people "like" the page to get deals. For CLA student ambassadors, we target students, but many organizations on campus "like" us as well, so we can be a way to get University information to students.
I find insights an interesting new trend in evaluating PR campaigns as well. It is free, but offers a lot of information.