Currently mesos provides a non-hierarchical resource allocation model, in which all roles are siblings of one another.
Organizations often have a need for hierarchical resource allocation constraints, whether for fair sharing of resources or for specifying quota constraints.
Consider the following fair sharing hierarchy based on "shares":
The hierarchy specifies that the engineering organization should get 3x as many resources as sales, and within these resources the ads team should get 2x as many resources as the build team. The implication of this is that, if the ads team is not using some of its resources, the build team and engineering organization will be able to use these resources before the sales organization can. Without a hierarchy, the resources unused by the ads team would be re-distributed among all other roles (rather than only its siblings).
Quota can also apply in a hierarchical manner:
See https://people.eecs.berkeley.edu/~alig/papers/h-drf.pdf for some discussion w.r.t. sharing resources in a hierarchical model.