Materialized views are a powerful tool in ClickHouse that can improve query performance and extend data management capabilities by storing the result of a SELECT query on data as it is inserted into a target table. This allows for faster retrieval of aggregated data without having to execute complex queries every time. Materialized views can be used to accelerate queries, filter out invalid data, route data to different tables based on certain conditions, and even perform transformations on data. They can also be used with JOINs, but this can significantly downgrade insert performance. By using materialized views, developers can optimize their data management workflows and improve the overall performance of their applications.