docs: Polish pre-aggregation intro

Author: paveltiunov

docs/pages/reference/data-model/pre-aggregations.mdx

@@ -6,10 +6,10 @@ redirect_from:
 
 # Pre-aggregations
 
-Pre-aggregations are materialized query results persisted as tables. Cube has an
-ability to analyze queries against a defined set of pre-aggregation rules in
-order to choose the optimal one that will be used to create pre-aggregation
-table.
+Pre-aggregations is an implementation of aggregate awareness in Cube.
+Pre-aggregation tables are materialized query results. 
+Cube can analyze queries against a defined set of pre-aggregation rules to 
+choose the optimal one that will be used to serve a given Cube query instead of going to the data source.
 
 If Cube finds a suitable pre-aggregation rule, database querying becomes a
 multi-stage process: