The reference node connects cad object from FreeCAD (Shapes, Edges, Faces) to output pins in pyflow. They are the importers to make FreeCAD data reusable.
The view3d node goes the way back. it creates a visualization of a shape in FreeCAD and creates a FreeCAD object which can postprocessed with classical FreeCAD methods or exported etc.
We habe a discussion about naming of this node type, so the concept may change again
in my video today I demonstrate the level of detail node. The idea is to have the possibility to switch between different representations of the "same" object on demand. example use cases are landscape, bolt, hole plate. In the example I only use cube, sphere and cone as placeholder for more complex shapes. For pointclouds and bspline surfaces I have a lot of algorithms to get simplified models, these methods will come soon.