I usually backup my itunes library file .itl. So I dont need to erase and resync everything on my iphone. I just recently reformatted windows 10 with a fresh copy because I upgraded my hardrive and forget to back up the preference file. But I had all the music backed up. So I simply dragged and dropped the music in itunes to relink the files, plugged in my phone and IT DIDNT NEED TO RESYNC? What is this madness? Is this a new feature with itunes? Usually It will say something along the lines of "your iphone is synced with another itunes library would you like to erase and resync" Im just wondering WHY it didnt happen? Possibly because my music library was identical to the one on the phone?