Pros & Cons: Humidity Switch for a Fantastic Fan?

We used to call them a "humidastat". Mounted on the wall like a thermostat. Used them in sensitive computer environmental areas where if the humidity would get too high it would bring on the air conditioning to condense water from the air to lower humidity and if temperature was too cool would bring on reheat to warm the air control temperature. Haven't seen or heard of one in years, but could try heating/air-conditioning supply sources.