When you first launch the camera app after inserting an SD card you'll see a warning letting you know of the change, and if you don't want photos or videos saved to the SD card it's a simple switch in the camera settings. And since you can't move all of your apps over to the card, it makes sense to start putting pictures and videos you take there, so that's what the camera does by default. When you put an SD card in your Galaxy Note 7, the phone will start to utilize it right away.