Hakkar does every 90 seconds a Life Drain, which hurts him, if you are posioned by a Son of Hakkar, but it heals him, if you are not poisoned.
If you are running at the moment, when Hakkar starts his Life Drain, you will simply miss it and you can do whatever you want during the Life Drain.
It's good for melee players (warrior, rogue), who don't have the time to run back for poison, so they won't heal Hakkar without poison and they can hit Hakkar during the Life Drain. It's also good for 1 or 2 healers, who can heal up the tanks, rogues, etc to max hp during the Life Drain.
To time the running correctly, you need a mod, that shows the exact time for Life Drain, for example CT_RaidAssist Multi. When you see, that 1s is left to Life Drain, start running.
If you are running at the moment, when Hakkar starts his Life Drain, you will simply miss it and you can do whatever you want during the Life Drain.
It's good for melee players (warrior, rogue), who don't have the time to run back for poison, so they won't heal Hakkar without poison and they can hit Hakkar during the Life Drain. It's also good for 1 or 2 healers, who can heal up the tanks, rogues, etc to max hp during the Life Drain.
To time the running correctly, you need a mod, that shows the exact time for Life Drain, for example CT_RaidAssist Multi. When you see, that 1s is left to Life Drain, start running.