Scala is widely used at Treasure Data for data analytics workflows, management of the Presto query engine, and open-source libraries. Some key uses of Scala include analyzing query logs to optimize Presto performance, developing Prestobase using Scala macros and libraries like Airframe, and integrating Spark with Treasure Data. Treasure Data engineers have also created several open-source Scala libraries, such as wvlet-log for logging and Airframe for dependency injection, and sbt plugins to facilitate packaging, testing, and deployment.