What do they do?

I am using Unity and it has a full implementation of rigid body Newtonian mechanics. I would assume other engines have that, too. I suppose Newtonian implementations can only be optimised, if anything. Other branches of physics are hardly of interest for most games. What are physics programmers hired for? I suppose someone who knows mechanics can use engines more cleverly but what is there left to code?

EDIT: Soft body physics.