The OpenGL state is updated during traversal
of the graph (top to bottom, left to right).
The effect of a parent applied to all its
child nodes; an operation performed on a group automatically propagates its
effect to all of its members.
In many programs, associating a
geometrical transformation matrix at each group level and concatenating
such matrices together is an efficient and natural way to process such
operations (recall lab 2)
A common feature, for instance, is the
ability to group related shapes/objects into a compound object that can then be
moved, transformed, selected, etc. as easily as a single object.