backup pictures, music, texts (if you want), contacts (if you're using G-Mail you don't need to). As Jst2Slow said (I think...!), anything you've downloaded from the Play Store (f.k.a. Google Apps, iirc) or from Amazon will still be there for you to re-download. You could move your apps to your SD card if you wanted, but I find it easier to just put back what I need, when I need it instead of having 8000 apps on the phone.