Bob,
The Auto-Track is so that if you pan over or touch the screen to look at something and forget to hit "Follow Plane" it will snap back to tracking the plane automatically. Maybe "Auto Follow Plane" is a better term. You can set it to automatically "follow plane" or Auto-Track based on parameters like if you are in motion or not and for a user defined period of time, 10 seconds to 10 minutes. IE, If you select While in Motion and 10 Seconds, the chart will only snap back to follow the plane or location if you are in motion and after 10 seconds. Like Ed said, if you want full control of the "Follow Plane" and don't ever want it to snap back to the plane, then just us the "Disabled" option. Just know that if you don't see you airplane icon on the screen, you will need to touch Follow Plane.
We had some pilots pan or touch an airport for info, the map will then stay at that point and no longer track the plane. They would then not be able to see their position til they touch Follow Plane. This is why we added the Auto-Track function. I hope this help explain it a little better.