Why do divers wear dive suits?

When diving, even in warmer waters, it is imperative that the body maintain a certain temperature.  If the body were to become too cold, blood and oxygen flow to the brain slows, which makes it difficult to think.  As a result, response time is compromised.  If a diver were faced with a dangerous situation but without wearing the appropriate exposure protection began to experience a dulling of the mind, this person might not have adequate time to make an appropriate decision, putting him or her in a life or death situation.