Again it seems that's a personal choice. Some think it does others think it doesn't. There isn't some strong objective indicator that will really convince everyone one way or another. I personally do not use one, which doesn't really say much one way or another for someone else.
Im using the glass protector always... My bf dropped his phone and luckily he had a glass ptorector on it. The protector went totally broken, but the phone itself was ok. Just a tiny "scratch" hairline on the edge of the bottom because of the impact. He didnt have a case to protect corners...
Yes you'll need one.
After only two month of use my iPhone 6S got 2 deep scratches. And no: there weren't any keys, knifes, coins, or whatever involved.
I use the Glass protector. The phone keeps falling off my hand while on the road and falling on Asphalt. Saved my display countless times. I would recommend