A set is a combination of dimensions, a group is a combination of values within a dimension. What are you trying to achieve? In V8 you can combine sets to create various unions.
I have built groups made up of certain products, collectively 6 groups with about 40-50 individual products per group.
I now wish to build a set around each group. For example only use transactions that include Group 1
Though this maybe a labor intensive option, a calculated field can be used to create a group. Then, this calculated field can be used in a set.
Hope this helps!