So like I mentioned, creating things in MoI is usually driven more off of key curves like profiles or cross-section curves.

This is also one method that can help you when deciding if a project will be good (and really quick) to do in MoI or not instead of in polygons.

If an object has very recognizable profile curves in it, then that will be a great candidate. Typically man-made objects fall into this area.

On the other hand if your shape has no easily recognizable primary profiles and instead has lots of little bumps and ripples, then it will fall more naturally into being being built with polygons/subd instead. Typically faces / creatures / character models fall into this area. (even though a face has a silhouette profile, it isn't the same kind of profile that I'm talking about because it rapidly changes).

- Michael