Well, actually, it doesn't.
As stated, you'd simply be adding an auxiliary drive on a laptop that has a bay for one. In this case it happens to be an SSD, but that's not all that important, at least if it's not going to become your main system drive.
It's the "inside the box" equivalent of plugging in a permanent external drive. The presence of a new drive just gives one new additional storage space, and nothing else.