A bain-marie is best used for keeping food hot. It is a cooking technique where a container with food is placed in a larger container filled with hot water. This creates a gentle, uniform heat that keeps the food warm without burning or overcooking it. Bain-marie is commonly used in professional kitchens and at buffets to keep sauces, soups, and other dishes warm and ready to serve. It is also useful for melting chocolate or butter, as the gentle heat prevents scorching or burning. However, a bain-marie is not useful for washing vegetables, basting meat, or keeping food fresh.