Some examples of shape key sculpting vs lattice? I understand the lattice modifier is for deforming complex objects and it's actually pretty amazing.  But the more I think about it, all the fine details can be done through sculpting shape keys.  Lattice seems to have static squares which you can scale infinitely to refine your detail, but I can't think of any reason to use it over just sculpting what I want in using shape keys.
My brain is probably not seeing the big picture here...  I'm mainly just focused on characters organic stuff.  Even if I wanted a bicep to expand, I can do it better with shape keys.
Shape keys and lattice are 2 completely different things in my opinion, generally you should think about shape keys (or bones) when you want to animate small details of your mesh, and Lattice (or Mesh Deform or Surface Deform modifiers) when you want to deform the whole mesh or a large part of your mesh.
Also, lattice is particular as it deforms only the part of the mesh that it contains, here is the kind of thing that you can do with Lattice that you couldn't do with shapekeys or Mesh Deform or Surface Deform:

Here is what it would give to have a boolean object that is latticed: