[lolinder]

Dryers typically are vented immediately outside via a dedicated tube and vent. That means that the air in the rest of the house never sees the moisture at all, so your whole-house ventilation system or dehumidifier doesn't need to work as hard.

[ajuc]

Thanks, now that I think about it that makes sense :)

[CalRobert]

Some driers, especially in Europe, condense the water in to a tank that you empty manually in to a sink. This is useful if you don't have an easy way to vent it and also shows just how much water is coming out of your clothes (multiple liters per load, sometimes!)