i think you can better post this question in physics topic.
btw i think that the addforceglobal adds a set force to the physics object global to the entity (thus effecting anything around it too, local would be only that one model, no matter how many near it).
but about the addtorqueglobal, i've no idea :$
now when to use addforceglobal, you could do it to recreate an explosion effect (make the force from the explosion point outward), or when you use a ragdoll, you could add a force to the point it shot.
hope it helped you out.
regards,