This is my favorite part too. With my own project for example, I had the agent integrate libgit into it so I could add source control to my IDE. Yes, I could have done it myself, but it would have taken me months of trying to understand the API, testing various things, and finally implementing it all. Instead, the agent did almost all the work (I still designed the architecture and how it plugged in). It took about two weeks calendar time and most of that time I was doing something else while the agent worked.
The thing is, before AI agents, I wouldn't have even attempted the work. I wouldn't have been able to afford the time.