Grading Groups

I have the comprehension of managing feature lines and grading objects in the respective Site and Surface. I do wonder when it really is a good scenario when to make different grading groups in the same site for the same surface might be?

My first thought (example) would be creating a proposed graded surface with feature lines and grading objects under a Site called proposed. Then adding a detention pond in the proposed grade and defining a new grading group "Detention Pond" under the same proposed site that would act as an infill. Seems logical to keep all proposed surface feature lines and grading objects associated with the proposed surface but detention pond grading objects would act as an infill.

Is this something close to a reason for different grading groups and if so what be the best way to void the area of overall proposed graded surface out of the infill of the detention pond?