[falcolas]

To add, humans emit a lot of moisture just by breathing. Also, modern code limits how much air can leak out of a house. It’s those leaks in old homes that let them survive without moisture control, because that leaked air would carry the moisture away.

[naravara]

Would one be able to achieve a similar effect by simply opening the windows on a regular basis? (Assuming all the other principles around good air-flow and ventilation were following in the building layout.)

[edaemon]

Yes, but modern humidity controls are able to regulate moisture levels while also reclaiming heat. That is, if you open all the windows your warm/cool air will flow out while fresh air flows in; an energy recovery ventilator will partially precondition the fresh air as it flows into the house, using the outgoing air as the source.

https://en.wikipedia.org/wiki/Energy_recovery_ventilation