On a boss with a 2 seconds swing timer, tclap brings it up to 2,4.
It's hardly noticeable during the fight. Healers are already stressed on precasting and the amount of overhealing doesn't really change. I'd say it removes 5% or so of the burst damage deaths, and over a long fight it reduces 15%-20% of the damage income on the tank.
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Spankadin in development.
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