The ultimate fail would be pretending jailers and then getting countered by the real ones. Thus, the prisoners must be told the truth when they still are with us and the truth problem makes a return. Thus, since we must be truthful, we can't avoid the issues that come with catching a meanie.
So really, it'd just be for the intimidation and hoping that meanies make a mistake and that caught townies don't get too mad cuz we made a 'lil lie. I still think it'd be worth it, but the gain even at best is not quantifiable.