File size becomes an issue as well. Use textures with texture mapping when you render.

If your object that you wanted to appear to be built out of stone but also just happen to be a box shape if you use most rendering software's texture tools (bump mapping) you can just use a simple extrusion with 6 faces, each side of a cube. However, if you decided to build the cube house out of individual bricks and if you just happen to need 1000 bricks your cube house now will have 6,000 faces to render. You also have a huge amount of either faces or objects (depending on how your bricks are made and textured) to deal with individually. There are probably easy ways to deal with groups of bricks for texturing but even so increasing a model's faces by 1,000 times for a small brick house - I'd choose 6 faces and find nice textures, texture maps, bump maps, etc. instead.