Tempered glass screen protectors are far more scratch resistant than normal plastic screen protectors. In a high impact drop, a tempered glass screen guard will crack but they act as a shock absorber helping to prevent your actual phone screen from cracking. They are five times stronger than normal glass and the smoothness and clarity of the tempered glass make the screen protector feel more like your phone screen than a plastic screen cover would.
Tempered glass screen protectors are also far easier to put on than conventional plastic screen protectors and you have less likelihood of bubbles and blemishes forming under the glass.
Tempered screen guards are an absolute must for any smartphone owner.