Why is there a filter on a dehumidifer?

In order for a dehumidifer to do its work it needs to suck air into the system and then release it, the fact that air is passing through the system constantly means it has the ability to clean the air as it operates, filters are included as they are cheap and you get a free air filtration system, there is little damage to the unit that can come from not using a filter, but they are added as an extra to help market the products better.