As moisture is present it can give rise to fungal or algea growth. This can rise not only to visual damage but also to detioration of the material. In addition aspecially funghi can give rise to health problem. Here are some examples given:

An extreme example of fungal growth in a bathroom

Two examples of algea growth on buildings


Examples of algea growth (green)  in a church in Portugal. This church had been flooded (melting snow)

Damage due to moss growth

Plant growth in the wood of a balcony in New Orleans