Sorry for such a newbie question, but isn't this type of posing destructive?
Is this only used for static renders, or is there an animation use for this posing technique within sculpting?
Not destructive per se, but since you have a sculpt at this point with lots of triangles and geometry, all high poly counts, a mess of topology, you can pose your character just for the sake of it, there's still no perfect retopology or edge flow that can be messed up, it's just a messy sculpted mesh. Maybe you are trying to mimic a concept art pose for example and that is why you pose your sculpt, but at this stage it is not the same as posing it with an armature, that comes later.
Typical bones and rigging animation is not ideal with sculpted meshes, the mesh is just to muddy and bad. For rigging you need clean topology, a mesh that has gone through retopology. Sculpting is for free flowing, concepting, good old clay fun to get your ideas out. Once you're happy with it, then you commit for reals and do some retopo. But in the mean time, since sculpted meshes are so static, those pose brush can help you achieve a good pose you want to test out.