Dehumidification can be very important if you live in areas of high humidity. High humidity in cooler temperatures gives you a wet clammy feeling and in warmer temperatures causes a wet sticky feeling and causes perspiration to stay on your body and soak in to you clothes rather than evaporate.
High humidity can also cause mold & mildew through out the house and even ruin very expensive clothes, fabrics, paintings & wall coverings.
All air-conditioning units take out some humidity when they are running but in very humid areas this is not enough and you need a dehumidifying system.
This can take out up to 15 times more water from the air than a standard system with very little operating cost penalty.