In a cloud a which is going up like a lift and bouncing you around, you would not expect releasing the controls to have a happy outcome. In clear non turbulent conditions I agree that you can let a well trimmed aeroplane fly itself, and when faced by a 'pudding stirring' pupil, it is often the only way to convince him/her that this plane can fly much better by itself. Having said that, it is a rare glider that is so well rigged that it does not enter a gentle banked turn after a short time. I suspect small single engined planes will do the same. But you are right, sometimes the best tactic is just to open the brakes,let go of everything and wait. Certainly the easiest way to recover from an 'unusual attitude'