Because it is massively more productive than when you have to manually approve what it's doing. You can literally leave it running for an hour and come back to a fully baked solution (or an unholy mess depending on how the dice rolls go).

I gave a talk about this earlier this week, slides and notes here: https://simonwillison.net/2025/Oct/22/living-dangerously-wit... - also discussed on HN here: https://news.ycombinator.com/item?id=45668118