If you just stick to the 'Pictures' tab of the Gallery you won't notice any difference, as all of the photos - SD card or not - will show up in the regular photo timeline. The difference is noted by a little SD card logo in the corner of the album, which is a little confusing at first. If you choose to keep that default setting, you'll notice that the Gallery app creates a separate folder for those images in the 'Albums' area of the app, which is separate from any other photos or videos you took before you put the SD card in. 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.
