You will see a caveat on Model import page: http://www.sweethome3d.com/importModels.jsp - that many of archive3d models cannot be imported.

Sometimes, though, the elements are specified and can be edited in SH3D (or other software). Other times they also appear fragmented/shifted/split. However, this happens not only in SH3D import but in other software (such as Blender) as well, whenever I have tried.

In addition, some of the model files are too big and have copyright limitations that makes them less than an ideal choice.

ok