If you use the editor scripts to create static mesh assemblies in the editor, the higher total triangle count of the final assembly the slower the creation process gets, to the point where you are waiting an hour just for the “mesh to be ready”, or “Loading *mesh” when trying to open it.
A tree with a total of 10 million triangles and 10 individual parts made me wait well over 1 hour before I could even use it!
I hope this is improved in upcoming releases..