The Morph deformer lets you apply the deformations from one geometry to another, similar to a Blend Shape deformer, but GPU-accelerated and giving to incorporate legacy CPU deformers in deformation chains without blocking the rest of the chain from GPU evaluation.
You can even use the Morph deformer as a quick way to retarget animation or mirror geometry.
A Morph deformer is added to the head on the left, so it can adopt the expression from the head on the right.