If you would be upset for it to get a scratch, you should put a screen protector on. It is jut a matter of time before the phone slips, something hits the screen or even a grain of sand in your pocket puts a scratch on you screen. GG2 will not prevent this.
If you love the look of the bare screen and feel it is a phone and a few small scratches are the cost of having a bare screen, go commando.
IMO it is not if, but when will your screen get scratched. I had a screen protector on mine within minutes of taking it out of the box.
Good Luck!