But then again, I don't care a bit about resale value, take good care of my phones, and upgrade my phone every year anyways. If any of those things are different for you, you might want a screen protector.
I'm currently using the Spigen GLAS.tR Nano slim. It's nice because it doesn't give off the orange-peel effect like found on the Invishield piece and barely noticeable, as a screen protector should be. Although it's extremely thin (0.5mm) it doesn't take much to damage it. In fact, I noticed a hairline crack in mine this morning and will be replacing it soon. The only downside, they're not cheap at $34.99.
It's not about having anything in your pocket, it's also about dropping. I don't put the phone in my pocket at all (left pocket is keys, right pocket is loose change and wallet). I have my phone on a holster. You never know when you'll drop it and you can't predict it either. There might be one day where you have it on the edge of the counter and either you or someone might knock it off by accident. Since you have it in your pocket, there might be a day where you'll pull it out and something bumps into you and it falls out of your hands.
No one can be too careful or prevent anything from happening. Just the way of life :/
I Verizon rep that I know had a tempered glass on his old phone and when he dropped it, the first thing that broke was the tempered glass. The screen on the phone was perfectly fine.