Document & Data on iPhone is junks files including browser history, cookies, logs, caches of photos and videos, database files stored by your apps. You’ll notice that some apps while being very small themselves have accumulated a lot of data. An example of this is shown in the image below, you see that the Facebook app is 109 MB whereas the Documents & Data stored is 1.2 GB. This 1.2 GB is what goes into your “Other” data.
These apps on iPhone don’t provide a way to delete Documents and Data, uninstalling and reinstalling the app is not the best option here. With the help of CleanMyPhone or PhoneClean you can delete the documents and data on iPhone without deleting the app itself.
Resource: http://www.fireebok.com/resource/how-to-delete-documents-and-data-on-iphone.html