DOCSP-37741 batchSize note (#7195)

* DOCSP-37741 batchSize note

* Adjusts text

* Adjusts text

* Adjusts text

Author: kennethdyer

source/reference/method/cursor.batchSize.txt

@@ -26,6 +26,18 @@ Definition
    most :driver:`drivers </>` return results as if MongoDB returned a
    single batch.
 
+   .. note::
+
+      If the batch size is too large, the cursor allocates more
+      resources than it requires, which can negatively impact
+      query performance.  If the batch size is too small, the
+      cursor requires more network round trips to retrieve the
+      query results, which can negatively impact query
+      performance.
+
+      Adjust ``batchSize`` to a value appropriate to your
+      database, load, and application needs.
+
    The :method:`~cursor.batchSize()` method takes the
    following field: