What is the significance of clearing_endpoints pointcloud?

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I am trying to understand ROS NavStack in more detail for modifying and re-using it in my applications. I stumbled upon this topic while digging around and could not completely understand the logic for it through the code. I would appreciate it if someone could explain it. Specifically, I want to understand how are the clearing endpoints calculated, what do they signify to the costmaps and how do they affect the obstacle costs around them.

If someone could link me to the right documents that would be appreciated as well, I could not find any documentation on ROS resource-page for obstacle or voxel layer.