From the Pancake.IO website (on the create account popup):
We value your privacy. We cannot view or edit data outside the folder we create. This is technically impossible for us to do - Dropbox enforces this themselves using something called App Folders. You can learn about App Folders on their website.
From the Dropbox API site:
A dedicated folder named after your app is created within the Apps folder of a user's Dropbox. You get read and write access to this folder only. Users can share content with your app by simply putting stuff in the folder from any of their computers or the Dropbox website.
So, the Dropbox API is used to able to access a sandboxed folder within your Dropbox