Hi !
I had a scenario when this DrillDownGroupLevel was helpful. In my report, I had created a custom group so that I could drill-down from it. I wanted to place static headers to be shown only in the drill-down data and not the top-level. I created the static headers in the main report and suppressed them in the main report. This is how I wrote my "Suppress" formula for the Header text object
If DrillDownGroupLevel = 0 then true else false
So in the main report it will be suppressed because DDGL will be 0, but the headers were showing in the drill-down!
Hope this helps you to understand the use of this
Regards