I was looking up 3D character models from various games (Battlefield 3 and DMC to be specific), just as research work and upon importing the model into Blender3D, I found that every part of the model was a separate mesh/object (head, armor vest, legs, hands, etc.).
This got me thinking: Why didn't the artist model them as a single object?
I think that would be better because:
You can save a few polygons in your model [*].
Doesn't animating separate parts [**] cause clipping issues as one mesh may not deform in sync with neighboring mesh?
[*] All parts were overlapping each other = the armor vest was overlapping chest polygons, which were not visible and thus wasted.
[**] All polygons and edges connected to each other.