It is possible to recruit a new general unit from any unit. The original unit is unaffected by this, so in theory, with enough money, it is possible to suddenly create 19 generals from a single pawn.
Since a generals battle value is about the same as a slightly cheaper knight unit, not much money is lost. Also, one can save upkeep while moving the knight unit to the front, so it might even out. Additionally, there is the chance to get a highly ranked general that considerably increases the strength of all units.
Personally, I find this idea kind of lame, but I successfully used it and wondered how others think about it.