The hardness of sapphire will make it resistance to ‘flaw initiation’ (aka starting to scratch) and its ‘toughness’ is how it resists fracture once a flaw has begun (cracking altogether). This strength doesn’t come without a bit of cost, Hall notes. “The density of Gorilla Glass is 2.54 g/cm3 while sapphire is 3.98 g/cm3. Given equal-sized pieces, Gorilla Glass will always be lighter.”
The counter-point to the greater weight is that Apple could use thinner pieces of sapphire due to its greater strength overall. This would result in weight and thickness reduction, which is something Apple is very conscious about. You may have noticed that the latest iPad Air was reduced in thickness in part due to its use of thinner glass and IGZO display panels.