Without a human in the loop? If you did that today, what percentage of the time would the change improve the software? What percent of the time would it make

Without a human in the loop? If you did that today, what percentage of the time would the change improve the software? What percent of the time would it make it worse (security, usability, accuracy, or whatever)? I think that today, this approach would work on some days. Some days it would fail, perhaps catastrophically. (I don't know the percentages, though. Does anyone have enough experience to comment?)