Having damp in your property can cause breathing issues for the people that live there.
Having damp can decrease the value of your property and make it more difficult to sell.
Damp that has been persistent in a property for a long time can cause major structural issues which could be very expensive to repair.
Damp can cause a huge amount of heat loss. Living costs with also be higher due to the higher use of your properties' heating.
Seeing damp in a building can make the rest of the property look worse. Painting or covering up the damp will only be a temporary fix and things will get worse.
A bad smell can really effect the whole presentation of a home. A nice atmosphere and lovely furniture will not matter if the air isn't nice and fresh.