For a humidifier, the better ones come with an outside sensor. That sensor adjusts the relative humidity level the humidifier is attempting to attain in the house so that on a really cold day, it doens't put quite as much moisture in the house so that you don't get condensation on the (probably) cold walls. Also, it automatically shuts off as the temperature outside gets higher. Mine won't let it run if the outside temp is 50F or higher. It works pretty well, and came standard with the AprilAire humidifier I installed. It is optional on others.
Removing to 50% in the winter might be great, but 50% in the summer might be too much (i.e., not attainable because of local conditions). So, adjusting it to the outside ambient temperature might be useful. If you don't, depending on where it is set, it might never turn off.