Plug-ins can build a mesh that is meant only for display by the graphics window system (which may or may not use hardware acceleration). The hardware mesh can be displayed without having to use the Mesh or MNMesh classes. This means that they are considerably cheaper on memory usage since the objects don't need to be instantiated in order to display the mesh.
The classes in the header files HWIndex.h, HWMesh.h, and HWVertex.h allow for creating, managing and displaying the vertex buffers, index buffers and the mesh.
A few cases when using a hardware mesh over Mesh or MNMesh might be useful are: