Yep, procedural content is one of the main goals. However, this workflow is also very useful for prepping a scene prior to runtime. For example, say you needed to place a bunch of trees on a terrain. You could create a little graph that 1) References a terrain mesh, 2) distributes some points on it 3) clones a tree model and places it in the scene. You save the scene, and away you go. No need to maintain a "Tree Placement" add on or something. Of course, there are benefits to the custom add on workflow, especially as the task grows in complexity.
As Victor suggests, the same workflow could be applied to Material and other Resource creation.