Lets say that I have groups 1. Also I have group A and B which is a sub group of group 1. Sometimes I may want to notify all of group 1 which would include group A and B. Other time I may only want to notify group B but not all of group 1. I hope that makes since.
Math test? I pick C as the answer. (Always pick C to word problems).
I don't use Enterprize, but I am the admin of a Workgroup. I don't think groups within groups is necessary, and it may make it harder to do what you want. You can just as easily set up groups that are specific and groups that are generic at the same time, and just have them overlap, and just pick the one that covers your subset.