The reason it's common courtesy is out of respect for the reviewer/maintainer's time. You need to let em know to look for the kind of idiotic mistakes LLMs shit out on a routine basis. It's not a "distraction", it's extremely relevant information. On the maintainer's discretion, they may not want to waste their time reviewing it at all, and politely or impolitely ask the contributor to do it again, and use their own brain this time. It also informs them on how seriously to take this contributor in the future, if the work doesn't hold water, or indeed, even if it does, since the next time the contributor runs the LLM lottery the result may be utter bullshit.

Whether it's prose or code, when informed something is entirely or partially AI generated, it completely changes the way I read it. I have to question every part of it now, no matter how intuitive or "no one could get this wrong"ish it might seem. And when I do, I usually find a multitude of minor or major problems. Doesn't matter how "state of the art" the LLM that shat it out was. They're still there. The only thing that ever changed in my experience is that problems become trickier to spot. Because these things are bullshit generators. All they're getting better at is disguising the bullshit.

I'm sure I'll gets lots of responses trying to nitpick my comment apart. "You're holding it wrong", bla bla bla. I really don't care anymore. Don't waste your time. I won't engage with any of it.

I used to think it was undeserved that we programmers called ourselved "engineers" and "architects" even before LLMs. At this point, it's completely farcical.

"Gee, why would I volunteer that my work came from a bullshit generator? How is that relevant to anything?" What a world.