Wei Zhu from Facebook Developer site had explained its benefits:
Since this library does not require any server-side code on the server, users can now create a Facebook application that can be hosted on any web site that serves static HTML.
This is a good move of Facebook. With this support, user may build a quick and efficient way to connect with the other people or businesses to make their idea for a Facebook Platform application into a reality. From this new move, users can create their API from any website by leveraging Facebook community relationships – which may encourage the API development and broader access to Facebook int the future.