A brief is worth writing down because you will reuse it, and because the act of writing the "come back to me" list is where you notice what you were assuming.
The handover check is the important one
Running the last prompt before a Bot starts costs a minute and catches the misunderstandings that are expensive later. If the summary that comes back is subtly different from what you meant: fix the brief, not the Bot.
Pair this with the access questions
A brief controls intent. It does not control capability: a Bot cannot be talked out of permissions it holds. See Connecting Bots to your tools safely for the half of this that lives in settings rather than in text.
What changes
Grok Bot is early and its approval and scheduling features are moving. Treat these as the durable shape of a brief and check x.ai/bot for what the product enforces for you today.