This is something I am going to start doing soon. The main reason is shelf wear. I hate shelf wear, because I love the glossiness of a brand new game. Also ideal if your home is not air conditioned, like mine isn't. In the summer, depending on where you live, that can wreak havoc on your games. Not everything I have is pristine, but what is, I wish to keep that way.
They make these for DVD cases, but I wonder, do they make them for blu-ray, or 3DS? Vita for that matter?