user as a parameter is an idea only used for safety systems. The idea is that if you are sending a unique user ID, they could tell you what ID is causing you problems or see that you are a multi-user developer.
It is 3+ years old, and I doubt anybody has ever had such an interaction with OpenAI. The latest Responses API description, so we know they just looked at it again, only gives benefit to OpenAI:
A unique identifier representing your end-user, which can help OpenAI to monitor and detect abuse.
It is not employed in any exposed utility or interface.