I've used auto-guidance for years, even networked it with my autopilot and at let it drive me around at 40mph (cruising speed of my offshore boat). Its just a general guide and Garmin never suggested that you can set your course and follow it blindly without having to worry about any debris or other boats. Also you can set the minimum water depth manually and the Garmin maps to mark rock piles and other under water obstructions, I know its not all of them but if you set the minimum depth to 6 o 10 ft then you most likely wont have to worry about stumps.

If you use auto-guidance most of you will like it, don't knock it until you try it.