I Have a Cheese Question

When is it possible to tell that blue cheese has gone bad? Does it even go bad at all? It kind of seems like the blue mold would out-compete any other invasive mold, that being how it got there in the first place. Not to mention bacteria (it is penicillium after all). Does it go bad when it winds up that there is too much blue mold? How would that be bad? It is basically what people want when they eat blue cheese.