MongoDB Atlas and DataDog work together to enable automation, elasticity, and scalability of modern infrastructure, allowing users to make informed decisions with real-time information. The new DataDog metrics tagging feature in MongoDB's integration allows users to organize and categorize their metrics using custom defined labels, which can be applied to tags on the DataDog metrics object. This enables filtering, grouping, and aggregating metrics in various ways, as well as setting alerts and dashboards based on tags. The feature is highly flexible and customizable, allowing organizations to adapt it to their specific needs and make data-driven decisions to improve application performance and infrastructure availability.