The HUD is required for takeoff and landing at Alaska Airlines in the -800, -900, and -900ER because it provides symbology to help avoid tail strikes. It is encourage or at least not discouraged for all other models. We also use the HGS for Low visibility ops in conjunction with the auto land system. Either or both can be used for low vis ops. But auto land used with the HGS gives us the lowest minimums which vary by airport.