How are complex mesh animations usually handled for optimization?

I don't know if this has one defined answer. I don't know much about animating or render optimization.

Imagine you have a character that has one complex animation that requires its mesh to be split into different objects, and several simple ones. For example a Transformer that has a detailed transform animation, but then moves without much complexity.

In Blender I would have the mesh split up into little pieces and make all of them unfold and move for the transform animation. For the other animations, these meshes would probably be in a hierarchy that allows leg movement, arm movement, etc.

However when moving this to Unity, it would mean lots of Transforms and internal geometry after the complex animation.

Does this have a performance hit?
Would it be better to have a complex mesh and transform hierarchy, and a duplicated simplified one and enable or disable them accordingly?

Thanks!