Root canal therapy is needed when the nerve of a tooth is affected by decay or infection. In order to save the tooth, the pulp (the living tissue inside the tooth), nerves, bacteria and any decay are removed, and the resulting space is filled with medicated dental materials, which restore the tooth to its full function.
The nerve of the tooth is not vitally important to its health and function after the tooth has emerged through the gums. The purpose of the nerve is to alert you to a problem by causing you pain and to give the sensation of hot and cold. Taking it out will not affect daily life. Not getting a root canal can lead to an infection or an abscessed tooth, and can cause swelling and bone loss.
Symptoms that may indicate you need a root canal include severe pain when applying pressure to a tooth, sensitivity to hot/cold, discoloration, swelling and tenderness of the gums, or a persistent pimple on the gums. However, you may need a root canal even without symptoms. The only way to know for sure is to have regular dental checkups.