WIS should provide a way for individual defenders to emphasize closing out on the perimeter or lagging off.
For example, if a team matches up against the Celtics they'd be fools to have defenders pressure Rajon Rondo @ the 3 pt line. However, the defender playing Ray Allen had better do exactly that.
Right now we have no way of accounting for individual match-ups in defensive positioning. I think adding this feature would certainly make defense a bit more relevant and realistic.