That's exactly it, a chain guide/guard to stop the chain rubbing on the swing-arm and also from trashing the engine cover if things move out of true.
when my swing-arm pivot bolt had worn away the nylon bushes in the swing-arm, allowing the assembly to move side to side, the guard took the brunt of the chain lash and although it did fracture (its only hard plastic) it prevented damage to the engine and swing-arm allowing me to just replace the guard, bushes and pivot bolt and not a complete swing-arm assembly.