OpenAI’s statements in response to the Millenium Prize (and related) disputes I think are a pretty obvious example of this in practice. One man’s “user prompts” is not another’s “reasoning trace scratchpad”.
This comment by Falserum on the mathematics research post articulates it well:
I'm pretty sure it is used for this; but rather than for anything nefarious, my guess is that this info is then fed to a classifier model to ensure that users of ChatGPT-the-service (as opposed to the OpenAI inference API) are actual humans, rather than agents trying to circumvent having to pay API pricing.