I wouldn't recommend leaving the helm if you intend to zip along at 20
knots. The situation can change too fast, and the possibility of hitting an
odd wave or another boat's wake can make relying on the autopilot a bit
risky.

I agree that in slow safe situations it might be pretty nice but at
fast speeds it would be like the old joke about the guy who had cruise
control on his van and went in the back while cruising down the
highway.
Thanks eveyone. I will continue to think more seriously about it.