*can reduce total bsp size due to less faces been writen to the bsp (a model has no caulked faces, so you only get the bits you need)
Minor nit: non-drawing faces are not written to the .bsp. However all brushes (including nodraw and nonsolid ones) are, with a couple of minor exceptions like origin. An ASE model generated from brushwork will have a face count very close to what the brushwork would make (slight differences may crop up due to t-juncitons).
There is another way models can also allow you to save space, if you repeat the same geometry in multiple places. A misc_gamemodel that has neither targetname nor scriptname doesn’t count against runtime entity count. This can be more efficient than using brushwork or a misc_model.