As lots of other users I have experienced this mysterious „other“ space you can see when you connect you iDevice to iTunes. I was not satisfied about any of the explanations you will find searching the web and specifically the apple support pages. On post at the apple discussion forum pages really fixed this issue for me (link). It seems like these „other“ stuff is mainly leftovers from the music synchronization where Apple seams to have problems syncing properly over a long period of time. I had around 2.8 GB of other stuff eating up valuable storage place on my devices.
- Simply go to General –> Usage
- there select Music
- swipe to the left (ios7, to the right other versions) and select delete
- restart the device by resetting it (hold down power and home button until device has shut down and you can see the apple icon again).
connect to iTunes, and voila in my case all the „other“ space was gone, the music was still in place. If it works for you too, spread this link so all the others having lost lots of space can regain their property ;-).