Level 10 of this skill is needed for the quest Athlete
It is unknown what function the elite effect "damage absorption" is supposed to have. There is no indication or evidence of it reducing any incoming damage.
It is unknown what function the elite effect "poison immunity" is supposed to have. It does not protect against the Unknown toxin that is applied with the Cultist knife by the Cultists. Considering the skill is in the game for way longer than the Cultists, it most certainly has not yet been considered to protect against their toxin.