The “assistant” role message is primarily to show the AI what it produced before as a record of the chat, or what you want it to believe that it produced in response to user input.
The AI that has been trained on chat would logically be given the last response it generated, so that the user could say “that’s not what I meant, I meant for you to duplicate the entire schema” and then the AI can not just understand the topic, but also can see its prior output and understand a different result than the one provided is desired.