In includes support for meshes, NURBS, 2D and 3D chains, polygons, materials, hierarchies, skeletons, animation constraints, Hermite splines, custom effects, user data.
The dotXSI Exporter that ships with XSI decided to cut through all the trouble that might arise from complex situations, by simply plotting all the shape animation.
The income of this behaviour is a significant increase in the final size of the dotXSI file, which -logically- should be avoided.
One nifty feature in the dotXSI Exporter is that it doesn't export shape animation keys that fall outside of your animation's time.