Unfortunately I don't have the link, but I remember a while back (about a year or two ago) there was an article posted on MR that one company did a drop study and found that screens actually cracked less when there was a screen protector on the device. Somehow it adds extra support to keep the screen intact.
No need to go crazy, either, I always find the cheap ones on Amazon (less than $10 for a three-pack to account for the first one you'll screw up with lots of bubbles) to be just fine.