The cavity may emit unpleasant odour and causes bad breath. This directly affects the normal social life.
Tooth decay may lead to persistent pain, which affects one's appetite, studies, work, sleep, or even general health.
When there is severe tooth decay, the bacteria may spread from the pulp to the surrounding periodontal tissues via the apex of the tooth, leading to inflammation or even the formation of dental abscess.
If a tooth is severely damaged that even pulp treatment cannot be done, an extraction is necessary. After the extraction, the neighbouring teeth may drift towards the empty space and cause malalignment of teeth.
If the teeth which support a denture had been extracted due to tooth decay, you should seek advice from the dentist whether the denture needs repair or a new denture has to be made.