Rene Ritchie, iMore:
The architecture is unnecessarily dependent on apps. If I create a document in Text Editor 1, not only do I have to remember the document I created but, if I want to access it again, I also have to remember the app I created it in. If I later switch to a much better Text Editor 2, my document doesn't switch with me. I have to either copy and paste every document from Text Editor 1 into Text Editor 2, or keep a list of which documents are where. That's a non-trivial amount of cognitive overhead. If at some point I move on to Text Editor 3, or delete (or switch devices and don't re-install) Text Editor 1, it gets even worse. I have to track my documents over multiple access points, and perhaps even re-install old apps just to get back to the documents locked inside. It's a mess.
What's funny is that Apple knows how to solve this. On the Mac, the iPhoto library can be accessed just like any folder on the filesystem, and on iOS the photo library is the same way. The problem is that Apple needs to define fixed buckets for documents the same way they've defined one for photos. I shouldn't have to remember if I created a text file in TextEdit or BBEdit.