"Optimize Game Objects" in ModelImporter inspector

MECANIM IMPROVEMENTS

Add a new option "Optimize Game Objects" in ModelImporter inspector. In short, this makes character rigs much faster.

When turned on, the game object transform hierarchy of the imported character will be removed and is instead stored in the Avatar and Animator component.

The SkinnedMeshRenderers of the character will then directly use the Mecanim internal skeleton, so that we can get rid of all the Transforms which used to be there, representing all the bones.

This option will improve the performance of the animated characters. It is recommended to turn it on for the final product. In optimized mode skinned mesh matrix extraction is also multithreaded.

When "Optimize Game Objects" is turned on, the user can specify a list of "Extra Transforms to Expose" in ModelImporter inspector. For example, if you want to attach a sword to the right hand, this acts as a mount point. The exposed transform is flattened in
the game object hierarchy, even though it might be somewhere deep in skeleton hierarchy.
http://unity3d.com/cn/unity/whats-new/unity-4.3