Avoidance behaviours seem to remove the body from further injury.
The role of expressive pain behaviours seem to have value primarily as social behaviours. That is, in crying out when hurt, you warn other members of your group of danger and at the same time call for assistance. So pain behaviours can be considered to also have a communications role, as well as a harm reduction role. These points are very logical for acute pain. While the meaning of acute pain is that harm has occurred, the meaning of chronic pain is ambiguous - it no longer signals danger of harm because the injury has occurred several months or even years previously.