Quote:

This is not just a helper for modelers - it's implemented into the game engines to improve the visual appearance and shading of 3d game models.



no, it's just a helper for modelers. you can achieve exactly the same look without smoothing groups but with split vertices.

in the end (since the hardware/directx/opengl don't work like that), smoothing groups always have to be converted to split vertices. it's just a matter of when this conversion happens.

most game engine's model formats are quite direct representations of the meshes the hardware needs. so the conversion already happens during export to the engine's model format. but i guess there are some engines which have smoothing groups in their format and do the conversion on the fly when loading the model.