From our list of fronts and stunts, we make two calls on every play. We make our calls TO opponent's strength (or wide side or tendency, and AWAY.
To determine which calls to maker, we lean heavily upon scouting reports, film, etc. Our scouting report also tells us that the calls (whether it is a straight front or a stunt) we make TO should be sound what the opponent does to that side, and the calls we make AWAY should accomplish the same objective on that side.
We generally give our signal caller about 4 calls TO and 4 calls AWAY, any one of which will mix with the other. We tell him that if he sticks to these calls, he can't go wrong. Now 4x4 = 16 combinations of defenses he can get by mixing these calls. While we stunt often, we pretty much follow the standard procedure of “pressing” when the offense is ahead of schedule, and “reading” when the offense is behind schedule.
Of course we would also have something for “sure pass”, short yardage, and various goal line situations.
WHY STUNT: A. Because we believe you need both “reading” and “penetration” defenses. B. To eliminate the “honey hole” on runs, and to achieve pressure on the passer.