I've applied gunting in an SD situation. Although I'd never bank on this 100%, but a lot of people throw sloppy "hay maker" punches, and gunting through that into an uppercut/push/more blocking/etc is certainly viable. It's happened to me a few times before, gunting is pretty effective in those situations.
Destructions, to me, should be reserved for an escalation in force. A responding officer or a jury will only see a dislocated joint, crushed base of the skull, etc and not see the situation in a completely favorable light for you. In other words, if there's ambulance ride-worthy injuries for the losing party, the winning party will still get tossed in the back of a patrol car regardless of who started the altercation. Destructions should be used very wisely.
Anyway, sparring is important. You get a sense of timing, realize when moments of opportunity arise, understand range, etc. You become a better fighter, instead of just being a better student.
Play with what works for you. You'll find that out once you start sparring, although I don't think applying destructions to a sparring partner would be useful.