A dehumidifier is a form of air conditioning which reduces the moisture levels in the air. This is good practice for health or thermal comfort reasons, or to get rid of odours caused by excess moisture in the air that cause mould and mildew to grow on walls and can cause serious respiratory health problems.
Dehumidifiers are used when moisture levels in the air are high, the technology within them removes the excess moisture, meaning that comfort levels in the room are being maintained.
Dehumidifiers are especially helpful if you dry laundry inside. When you hang the washing on a clothes maiden, the air automatically becomes damp and overfilled with moisture. If the excess moisture is not removed from the room, the room can become damp and mould can start to grow on the walls. They are also used during the winter when condensation starts to form on windows, a dehumidifier will draw away the condensation. They are also good for helping reduce allergies such as Asthma.
A dehumidifier should never be placed against a wall or any furniture, you should position the dehumidifier at least six inches away from any objects etc.