So you've NEVER had a sketch, proof of concept or prototype end up being a part of the final product? Now you're stuck with a piece of crap that was implemented expecting to be thrown away, but then because of time and money constraints it's now a load-bearing (heh) part of the application.

It also takes more time for humans to build prototypes and PoCs than doing the same with an agent. Iteration speed and time-to-market matters more and more (case in point: mobile games).