Germany

A dehumidifier can help a lot when the room is barely heated. This is also the case when insulation of the building is bad. Some apartments will always be humid, even when opening the windows everyday. In those cases a dehumidifier will do the trick and you'll get about 2 - 3liters of water out of the room within a couple of hours.

That makes sense if you want to ventilate their air anyway. After all you need to get rid of CO2 inside as well. Fun fact: You don't need to worry about the lack of oxygen in that context. If the oxygen level have dropped from from the normal 21% do 17% because the oxygen (O~2~) was magically removed you'll still be perfectly fine. But if those were converted into 4% CO2 that will make you sick.

Anyway: My point is that a dehumidifier is more often more efficient because it doesn't involve wasting warm air. It's also a fairly efficient heater. Dehumidifying, i.e. turning vapor into liquid means that you get the energy used for evaporation back. It's essentially sweating in reverse. With a typical dehumidifier that means you get about 2 Joules of heat for every Joule of electricity used.