Backups should be able to be merged with data on the phone. The use case is I want to travel overseas but I don't want various border control entities to make copies of my phone contents, so I back it up and reset the phone to factory defaults. Then I go on my trip and take pictures and receive texts and etc. When I get home I should be able to merge the pre-trip backup and the during trip stuff into a single set of contents on my phone.