I almost find this feature pointless for the Automatics. It's useful when you're teaching someone how to start/stop on a hill while they're learning manual. I learned how to drive manual in a car with out it, so I absolutely hate this feature when I'm driving and have it disabled. However I don't want people burning out my clutch while on a hill so I enable it when there is a learner behind the wheel.
HSA is actually designed to prevent your vehicle from rolling for 2-3 seconds while on a hill. Let it be descending or ascending from a starting position.
The feature is useful for some, and in some situations. I'm just glad that there is the option to disable the feature unlike other vehicles I've driven where you cannot disable it for "safety reasons".