When dealing with complex concurrent requests, Snowflake's multi-cluster virtual warehouses offer a solution by providing fully-automated scaling for concurrency. These warehouses allow multiple clusters of compute resources to be used, enabling improved performance at lower costs compared to increasing the size of a single warehouse. The two modes available for multi-cluster warehouses are Maximized mode and Auto-scale mode, with auto-scale mode being more complicated but also offering better scalability benefits. Multi-cluster warehouses are particularly useful for building in-product analytics or apps with multiple users, as they enable efficient querying and processing of large amounts of data without the need for manual scaling or significant upfront costs.