Worse, for those 12 parameters (invariably booleans or if you are lucky enums) functions is that usually only a small subset of all possible flag combination is

Worse, for those 12 parameters (invariably booleans or if you are lucky enums) functions is that usually only a small subset of all possible flag combination is tested (or even meaningful). Worst part is when the flags are directly or indirectly under user (or configuration) control and the application can go into uncharted territory. Worse still, good luck refactoring those functions when you have no idea which combinations are actually meant to be supported and what their original semantics where.