My mind doesn't develop a mental model of that code, I don't know where the relevant parts are, I can't quickly navigate through it and I have to reach the LLM for every small change.
Which is why I like Copilot style editing more than agents as a working model but agents are just so much more powerful and smarter thanks to everything available to them.
If you use cursor, cursorrules can be a good way of doing this.
I will keep using LLMs for 1 week greenfield hobby projects that I don't plan to revisit. But no matter how good LLMs get, I will never use them in my dailyjob, otherwise, I risk losing touch with the codebase.
It's a good, very digestible paper, in my opinion; well worth the read.