I do read it. In my experience the project will quickly turn into crap if you don't. You do need to steer it at a level of granularity that's appropriate for the problem.

Also, as I said, I've been coding for a long time. The ability to read the code relatively quickly is important, and this won't work for early novices.

The time saving comes almost entirely from having to type less, having to Google around for documentation or examples less, and not having to do long debugging sessions to find brainfart-type errors.

I could imagine that there's a subset of ultra experienced coders who have basically memorized nearly all relevant docs and who don't brainfart anymore... For them this would indeed be useless.

Same way you test code you wrote by hand. In-place and haphazardly, until you have it write unit tests so you can have it done more methodically. If it hallucinates a library or function that doesn't exist, it'll fail earlier in the process ; compilation).

Because it does what I want it to do?

Not sure how this is so hard to understand. If you have closed source software, how do you know its's working?