This is an optimization to handle the use case where a leaf node contains points that all end up in the same voxel that they started and no points are inserted or deleted from that leaf node. Instead of creating a new AttributeSet, allocating new AttributeArrays and copying across the contents of the old ones, it would be faster to simply steal the data from old leaf node.

This is a relatively trivial optimization and doesn't require any API or ABI changes.