The reason for on/off switches on cruise controls is design of the system. It's a module bolted on to the throttle control and it has its own power supply, so it can be switched on and off. There's no usability reason why it's set up that way.
The way to tell if goronzola or bleu cheese has gone off is color, texture and smell. The molds will change color, the cheese will change color, it'll get mushy, and it smells different. When in doubt, throw it out.