I can give you an opinion on this based on personal experience--
I have owned several iPads in my life: iPad 2, iPad 3, iPad Air, iPad mini 3, iPad Pro 9.7", and now iPad Pro 10.5". I have never used screen protectors on my iPads because they're not sliding in and out of my pocket all the time like my phone does, and they always have a cover on them when not in use. I do baby them though--I've always kept my iPads in some kind of case, never use them with dirty hands, never wipe them off with anything but clean microfiber.
Except for issues I've had with screens coming with hairline scratches already on them, I have never put a scratch on an iPad screen myself UNTIL I started using the iPad Pro 9.7" with Apple Pencil. I must have gotten a piece of abrasive grit or something caught in between the screen and the Pencil, because I did manage to put a small scratch in the screen while sketching. Nothing major that I could feel with my fingernail or anything, but a scratch nonetheless.
Once that happened, I put a tempered glass screen protector on the iPad Pro 9.7", and I also put one on my 10.5" as soon as I took it out of the box. Yes, it cancels out the anti-reflective effects of the iPad's screen and it makes the Pencil a bit more slippery, but I don't care. Scratches in the screen are something I will avoid at all cost. I want peace of mind, and I want to be able to sell the iPad for the maximum amount when I upgrade.
EDIT: Case in point--when I sold my iPad Pro 9.7" on Swappa, the buyer commented on its pristine condition when he closed out the sale--he was very impressed. I suppose he didn't notice the small scratch or didn't care about it since it was a used iPad.
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Whelp, that about does it. Guess I'm not taking my screen protector off. I also don't agree that these screens don't pickup scratches. My iPhone invariably gets micro scratches if I don't use a screen protector. It's not so much the glass as it is the oleophobic coating on the glass, I think. And speaking of which, that's the other thing. That coating doesn't last forever, which means after about half a year the screen starts getting smudgy.
Love the non-screen protector feel though. It's a shame there aren't better glass screen protectors out there.
Anyone who says their iPhone or iPads have never picked up at least hairline scratches even after daily heavy use has never inspected their iPhone or iPad under the kind of lighting that exposes them. Most of the time, if you look at the right angle under bright light, you will see at least hairline scratches in the oleophobic coating. That's just the way it is with no screen protector. It's way better than it would be with a plastic screen though, and some people just don't consider those to be real scratches.