Authentication is easier. Application access becomes simpler as well, since even a JS tool running on a browser can connect and check your site. That also means

Authentication is easier. Application access becomes simpler as well, since even a JS tool running on a browser can connect and check your site. That also means not running an additional S/FTP server, which frees up resources to serve content (which would include responses to API requests). Plus you get more fine-grained control of exactly which features are displayed to applications and this could include number of hits and other statistics (if they chose to implement it).