The Aggregate tables are the ones that get values initialized in them as and when the related fields in the other tables get updated. This type of automatic updates to frequently used measures help you in speeding up the queries. If there is a column for number of products produced for every month and you often want to have the summation of the number per year and average for every year often for all the queries, the aggregate table created will have the option to give you that value without computations every time. Siebel Analytics server gives the added advantage that the queries need not be aware of the readily available aggregate table names. If this was the case the SQL queries and the entire design might become complex.