It's a bit difficult, as I have done this in my last job with R&R Report Writer and I do not have access to that here in my new job, but I'll try:
I think, it's a bit equivalent to the Sum/Break function of Query Reporteer. But in Query Reporter there is no way to get _only_ the summary lines. In R&R I could press a button for "Suppress record lines" and only this line has been shown, filled with sums or where only field were mentioned, the fields were filled with the latest field values.