The ability's small cooldown is useful for ability rotation when aiming to gain adrenaline. It is often useful to use Wrack in alternation with other abilities to avoid having most basics on cooldown.
Another good use of Wrack is in combination with Impact against stunned opponents. As Impact stuns targets, Wrack will then provide an extra 32% damage. This does not work on most bosses as the majority of them are stun-immune. This can also be done with Ice spells.