The Facebook Events app looks to take advantage of the core principle of social media and social media marketing.  That is building and nurturing connections.  

What better way to build your brand loyalty than giving your Facebook followers exclusive access to events, that not only allow them to share their experience with each others but also with you.  We talk about engagement a lot in social media, likes, comments, re-tweets etc but it doesn't get much better than getting people to physically turn up.  

While there are a few similar apps available, Facebook's existing audience, understanding of social media and knowledge of its users interests and habits puts in a great position to make this a hugely successful app.