Glass screen protectors supposedly protect your phone from impact. A youtube comment by McZidanne sums up this idea pretty clearly:
The thing about tempered glass cover isn't the protection they offer. It's the fact that they give in easier than the screen, so when a surge of energy is released into the phone as a result of a fall, the tempered glass absorbs that energy and protects the phone from having to absorb it.
However logically with my limited understanding of Physics this does not seem to be a phenomenon I can understand. A thin hard object shouldn't be able to reduce the force applied on the screen nearly at all, or can it? At least a plastic screen protector is soft, and can thus (theoretically) change the angle of the force partially (even if too insignificantly to be useful), but something hard as glass seems to me to be even less capable of protecting against impact. Am I missing something about the material properties of tempered glass?