Dr. Richard,
Sometimes a good back up plan can be intitiated just to add some variety or reengage students who've lost focus for wahtever reason. Of course, a great use is when there is extra time to fill and the regular lesson is complete, or when things just don't go as planned - that's when the loe bak-up plan or "Plan-B" can be used to ameliorate the situation.
Barry Westling
