Why "Documents & Data" is consuming so much space in iPhone? Looking at the iTunes storage information associated to my iPhone 5S, it seems that Documents &amp; Data occupies around 3.5 GB of space.



On the other hand, on the iPhone, Documents &amp; Data stored on iCloud are around 300 MB (so much less).



Which value should I trust? Moreover, if iCloud just requires 300 MB to store documents and data, what is the meaning of the 3.5 GB data that appears on iTunes?
Well it is normal. You can refer to this: https://support.apple.com/en-us/HT201656

If storage amounts on an iOS device differ from what you see reported in iTunes


  Since iTunes categorizes cached files as Other, reported usage for
  Music or Videos might differ. To view usage on your iOS device, go to
  Settings > General > Usage > Manage Storage.