Hi,
    Theirs no need to root you're nexus 7 tab.On Google play download a app called nexus media importer its about a couple of quid and plug n play virtually no setting up it recognises automatically when a flash drive is inserted & The app is open.I have no connection with the developer but just got it my self and then read this thread.Hope this helps as it certainly won't affect any warranties like rooting would if the tablet goes up the old swany during rooting ect .