If ever you run short of storage space, or if you just don't feel like contemplating this yellow portion of the iPhone data usage showing in iTunes, you can use DiskAid to clean it up.
We have recently posted this radical and foolproof tutorial designed to reclaim all possible storage space through a factory restore. This method causes some data sets to be moved out of their normal locations but it provides a very good incentive to get healthy - and really think about what your iPhone really needs to carry on.
Keep in mind that some files show up as Other only because they do not fit in any of the media categories metered and are defined as Other on purpose. This is for example the case for users having iTunes Match enabled as this creates the folders CloudAssets and Purchases - that don't fit into Audio, Photos or Apps categories. Further,
Also note that although the successive changes in iOS, back ups, restores and syncs might orphan files and generate unnecessary files over time, basically every file present in an iOS device is there for a reason.
Further, be aware that this is an advanced topic, only proceed with great care!*
How to Proceed
The following links to an article describing a method that will clean up two folders within the Media partition that are likely to host unclaimed files: How To Remove “Other” Data From Your iPhone. Basically, the idea is that successive syncs have left files that are not being referenced by their native applications. The workaround consists on deleting (having backed up the data prior) the contents of the Photos, Music and Video folders and re-syncing and in doing so sparing all the files that were not deleted automatically by the system.
Alternative places where to look up for files gone wild in the Media partition include 'Recordings'. The illustration below clearly shows a discrepancy between what the iPhone built-in Voice Memos app shows, and what the folder containing the app's recording reads in DiskAid.
The good news is that by copying the whole folder to your computer (before erasing the sound files) there is a fair chance to recover some recordings you might have thought were lost. Anyway, the deletion of unmatched files form the iPhone file system will undoubtedly free the equivalent amount of space.
If you have found any other noteworthy and unwanted files clogging your devices' storage space please contribute in the comments below!
*We cannot stress enough the importance of keeping a back up of your data and iPhone media while attempting to access and make changes within the iOS file system using DiskAid. A full backup iTunes will help you restore your existing text messages, contacts, call history and settings, the pictures will also be safeguarded, but in order to keep a backup of your music, video and other media you MUST make sure they are currently in your iTunes library, and if not you should use DiskAid to copy your media library to iTunes.