Hierarchical placement means that you can place your agent allows us to place the agents in hierarchical local space instead of world space.
For example, you have several battleships there are 2 ships in scene, and each ship has some agents on the deckit. These agents are walking and doing something , on their ship independently while the ships are moving respectively. At this time So the agents on deck will naturally moving move along with ships also. If we put our while perform their own behaviors. To achieve this, we just need to put the agents into each ship's local transformation space (Maya parenting)
Agents are acting on moving ships
To parent the agents initially into each ships child space, it just need to put their associated place node under ship transform node which means a child node of ship node, the agents who are populated from this node will automatically be the children of ship. These
Then, these agents will act in their parent's local space respectively.
...
For achieving this, the only thing you need to do is parent your place node to its parent. Like this: 
Once you place your agents
Parent place nodes to different spaces
Once agents are placed, they will automatically host to the same parent of place node.
Hierarchical placement, (left) before placing; (right) after placing
...