Any benefits to a soft terrain tire?

Actually, soft terrain tires are made of a harder rubber compound, as they just need to dig and not stick as much. Hard terrain tires are made of a softer rubber compound to stick to harder surfaces (hardpack dirt, rocks, etc). From a wear point it is better to have a harder compound, but if you ride lots of rock (say, like Moab) then you will have a hell of a time because you have less traction. Soft terrain tires also have taller knobs with wider spacing, so they lack the contact area to get good traction on hard pack.