I think it taxes your brain in two different ways - the mental model of the code is updated in the same way as a PR from a co-worker updates code, but in a minute instead of every now and then. So you need to recalibrate your understanding and think through edge cases to determine if the approach is what you want or if it will support future changes etc. And this happens after every prompt. The older/more experienced you are, the harder it is to NOT DO THIS thinking even if you are intending to "vibe" something, since it is baked into your programming flow.

The other tax is the intermittent downtime when you are waiting for the LLM to finish. In the olden days you might have productive downtime waiting for code to compile or a test suite to run. While this was happening you might review your assumptions or check your changes or realize you forgot an edge case and start working on a patch immediately.

When an LLM is running, you can't do this. Your changes are being done on your behalf. You don't know how long the LLM will take, or how you might rephrase your prompt if it does the wrong thing until you see and review the output. At best, you can context switch to some other problem but then 30 seconds later you come back into "review mode" and have to think architecturally about the changes made then "prompt mode" to determine how to proceed.

When you are doing basic stuff all of this is ok, but when you are trying to structure a large project or deal with multiple competing concerns you quickly overwhelm your ability to think clearly because you are thinking deeply about things while getting interrupted by completed LLM tasks or context switching.