By offering this to devs, they can then use that data to enrich their own apps. Naturally, users will still need to give permission for access to the data upon installation, as per normal.
The API is a REST-based Web service API that queries Sony’s Lifelog platform to return usable information in JSON format. Sony suggests it could be accessed for things like using lifestyle activity data to make recommendations in a third-party app or service.
If you’re a developer interested in learning more, you should check out this page.