when u want to see sum of sales by different dimensions like country, product, category,etc u go for cyclic group.
when u want to see sum of sales by country, state, district, city , etc u go for drilldown.
In drilldown we will have bars for each country on clicking a countries bar we sill get state level data of the particular country alone. Like u have made a selection in country but in cyclic group it is not the case u see data in a differnt dimension.
-Sundar
