Eager Aggregation re-writes the queries over star joins, accelerating performance.
Majority of the queries in BI are star queries that operate on large amounts of data, and often run very slowly. They are difficult to optimize because analytical views to route such queries must materialize joins. The analytical views themselves are huge, and cannot be refreshed incrementally.
When you enable Eager Aggregation in conjunction with Analytical Views, the performance of star join queries improves by factors of 20 to 800+, depending on the workload and cluster characteristics.