What does Beacon give me that Facebook analytics doesn’t?

Facebook only reports on the success of your post on Facebook, the number of Likes, Shares, and reach within your Facebook audience. By default Facebook does not report on anything that happens after a link has been clicked on your Facebook post.

Beacon shows you what happens when people click through a link in a Facebook post and reports on website activity; traffic generated from that post, visitor time on site, number of page views per visit, along with user journey information and conversions.