When we export a model to MDL format for the simulator, the exporter combines parts that are the same materials. All the work we did to keep parts separate is welded anyways in the export process. Also the parts are triangulated, losing their quad layouts.
When you reverse engineer/open your model after exporting to MDL format, its unrecognizeable... 8-0
I found out later in my days that combining various parts into one mega part made sense and I started doing that. Sometimes I map the parts before I combine them. Then its easier to animate them, etc. One big happy part.....