You don't use 1. Advanced blocking is sending some larger number of soldiers or elites or other combination to tie up a camp long enough for another general (or two) to walk through, engage the real target camp, (a leader camp), defeat the leader and release your blocking wave before the blocking battle ends.

Typically you need the blocking wave to go 5+ rounds, or longer, to ensure the leader camp battle ends first. If it does, all the bandits in that sector disappear, and your blocking wave troops return to their garrison unharmed.