The takeaway is that this could be harmful, weakening parent-child bonds and preventing children from learning how rules work. If I tell my child that the cops will come and arrest him if he doesn't brush his teeth, he will never learn why he should brush his teeth.
On a similar note, when I was a kid, the lifeguards at my swimming pool told us that if we ran on the pavement, we would fall and crack open our skulls. I took that promise quite literally, and when running from one end of the pool property to the other, my legs would magically gel into walking rhythm the second I passed off the grass. This didn't stop me from understanding why I shouldn't run on the cement, but I don't think that the adults realized how seriously I took this claim, and that maybe it wasn’t necessary to be so morbid. To this day, I cannot run on pavement when I'm at the pool. I was a lifeguard in college and I'm sure I would have gotten in trouble if there was ever an emergency that needed my immediate attention. I can picture myself walking to an accident. "What are you doing?" People would say. "Hurry up!" "Sorry," I'd reply. "I don't want to crack open my skull." Color me traumatized!
Remember any of your own parents' little lies? What lies have you told your children to get them to behave?