Why do dentists use anaesthetic and sedation during hospital procedures?

If some one were to drive a drill into your mouth, rip out a tooth, cut your mouth with a scalpel and in general muck about with pointy and painful things, not only will this hurt like God has forsaken you but while you are in pain you may thrash about and make it difficult for them to work and possibly do serious damage to your health, by the same token you might freak out from shock and harm the dentists, and if you go into shock it is quite possible to die from it.