A while after I got my GS5, glass protectors started to become popular but I didn't really see the point. My experience with screen protectors had previously been one of poor alignment, fun with bubbles, peeling, and the terrible feel of the plastic ones I'd used on other devices, compared with the great-feeling Gorilla Glass.
By the time I replaced that phone, it was nearly 3 years old and and had never had a screen protector, and while the silver paint was worn off some areas of the plastic trim and I'd replaced the battery cover, you could only see these "micro-scratches" on the screen in certain light, if you looked really closely.
But, my wife had put a glass protector on her iPhone when she got it, and I was pretty impressed by how much better it was (looks, installation, and feel) than previous protectors I had used. It wasn't enough motivation for me to ever get one for the GS5 that was over a year old by then, but I figured why not put one on the G6 right off the bat - it certainly doesn't hurt and cost me about $10 for 3 so I can pretty much just put a new one on every year.
Here is an interesting article, a couple years old now (and the actual truth is probably somewhat different from what it says), but it puts forth a couple arguments against tempered glass.
Why We Don’t Sell Tempered Glass Screen Protectors | Mobile Outfitters Blog: Our thoughts on mall kiosks, business and tech
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