fixes MicrosoftDocs/sql-docs/issues/4787 -- clarify query optimizer behavior

Author: WilliamAntonRohm

docs/relational-databases/polybase/polybase-guide.md

@@ -87,7 +87,7 @@ PolyBase enables the following scenarios in SQL Server:
 
 ## Performance
 
-- **Push computation to Hadoop.** The query optimizer makes a cost-based decision to push computation to Hadoop when doing so will improve query performance.  It uses statistics on external tables to make the cost-based decision. Pushing computation creates MapReduce jobs and leverages Hadoop's distributed computational resources.
+- **Push computation to Hadoop.** The query optimizer makes a cost-based decision to push computation to Hadoop, if that will improve query performance.  The query optimizer uses statistics on external tables to make the cost-based decision. Pushing computation creates MapReduce jobs and leverages Hadoop's distributed computational resources.
 
 - **Scale compute resources.** To improve query performance, you can use SQL Server [PolyBase scale-out groups](../../relational-databases/polybase/polybase-scale-out-groups.md). This enables parallel data transfer between SQL Server instances and Hadoop nodes, and it adds compute resources for operating on the external data.