In Magento CE 188.8.131.52 in database there are two separate tables for example In case of order, data store in
sales_flat_order_grid tables but if you see column then
sales_flat_order_grid is nothing but subset of
sales_flat_order, why magento need two separate table to manage order data as
sales_flat_order is enough?
same thing applicable for shipment, invoice, credit memo and etc.