Pads the pressure points by taking the shock from a fall. No question in my mind that it will prevent broken screens and backs. Not in all cases, but it will help.
What would you rather have hit concrete, the corner of your phone which is taught against a piece of glass, or the corner of a padded rubber bumper?
Plus it keeps the front and back raised, which will help, but not prevent, hitting those surfaces on flat ground.
Plus it feels great in the hand.

(and pads the sensitive lower left seam from bridging the antennas together causing interference)