Grouping Question

[rhythmz]

My shop is just now implementing 8BI from 7.3 and I have seen instances where a Data Item can be defined as:

total(product_count for region, store, dept, product_line)

I am used to setting associations in 7 at the bottom for the calculation definition window to one grouped cplumn. However, it appears in 8 that the above mentioned is a "multi-group" method that I have not encountered nor understand.

Since only one value is returned, what is this advantage\disadvantage and can anyone point me to further references that I can experiemnt and research myself?

Thank you very much!