Poser stores the geometry in the PZ3 if it was embedded anyway (often the case with hair and props) or if you've used the Group tool on it, otherwise it just puts a reference in. Most PZ3s seem to be over 20MB, and 100MB is not unknown. If you want to reduce the size try turning props and hair into external geometries (there are tools and tutorials, though I can't remember where) and, in the case of Millennium 3 figures or the RDNA MicroCosm, make sure you don't leave unused morphs injected.