I tried to design some possible Common Groups realizations here, including hierarchical (hard to create, easy to manage) and non-hierarchical (easy to create, hard to manage) solutions.
I my opinion cumulativity brings a lot of excess freedom to a system (easy to create, hard to manage), but, well, it cannot be taken back. Gin of excess freedom was released from the bottle =)
We always afraid of such a gins in scene content management systems, because they add control difficulty levels.