Aggregations are crucial for processing large amounts of time series data. However, improper use can lead to inefficient queries. To optimize aggregation performance in InfluxDB using the Flux language, users should avoid aggregating too early or too late and take advantage of pushdown patterns that allow the storage layer to perform more work. By doing as much filtering as possible before applying aggregations, waiting on transformations until after aggregations, and utilizing pushdown patterns, users can significantly improve query performance.