Some new functions appear on iOS 9.0 beta recently. But when updating the system to iOS 9, most of users meet the issue that it may delete some part of APPs to make room to continue the update. After updating, these deleted Apps will be installed on device again.
However, this condition only appears at iDevice which has limited room. When meeting this issue, there will be a windows popping up to inform users, who need to allow device deletes some part of APPs. Fortunately, the deleted APPs will be installed on iPhone/iPad automatically after finishing updating.
Many users with the smaller 8GB and 16GB iPhones reportedly had difficulty fitting the last upgrade onto their mobile devices. And while iOS 9 is only a fraction of the size of iOS 8 (they're 1.3 GB and 4.3 GB, respectively), Apple is clearly trying to nip similar complaints in the bud this time around.
Then why not use FonePaw iOS Transfer which can help you transfer the files from iPhone to computer such as videos, pictures, books, etc. to help you make a room safely. If you discover such a mass of files which are useless, just delete them including photos, movies, audio books, music videos, etc. through FonePaw iOS Transfer directly. What’s more, don’t forget to back up your iDevices data before updating to iOS 9, in case you lose data.