During the breeding season, most breeders drop their temps at night down into the low 80's. Rather than manually do it, you program the night drop to drop a certain amount of degrees at a certain time.

for example, at 9pm, if my thermostat is set to 93, and i want to drop it to 85, it would set it to drop 8 degrees at 9 pm. then at 9am, the voltage kicks in and bumps it back up to 93 to simulate night and day in real life.