Why am I Processing Index Separately?

Someone asked me why am I processing index separately in my earlier post. Why didn't I do it inside the first measure group foreach loop.

Yes, it would have worked.

There is a reason for splitting it up, is because that we have a measure group with billions of rows. Building aggregations on that measure group will take some time. I do not want to hold rest of the measure group partition processing.

Therefore I process the cubes first and make them available to users as quickly as possible and then build the aggregations. I have informed the users that some of the reports might not run as fast as you would expect straight after refreshing the data, until the aggregations are rebuilt.

Thanks
Sutha