For clients and freelancers both.
Whatever you're shown during a BotPool project is confidential and stays between you and the other party. That covers client data, project details and anything proprietary, and it doesn't expire when the project ends.
If you're the freelancer: you can normally show completed work in your portfolio. The exception is a client who has asked for confidentiality or exclusivity — then it stays off your portfolio.
If you're the client: say so before work starts if the project is sensitive. Retrofitting confidentiality after delivery is a conversation nobody enjoys.