All depends on strat and your dps. Fights like Sha of Pride I solo all the adds everyone focuses on boss i use them for procs on boss for more holy power seeing as I solo heal myself on most fights.
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The hit the cloak absorbs doesn't give veng so you would need something to get enough veng to equal the amount of dmg the cloak brings even on single target.
Not sure what mechanics are even gonna kill you that you could have prevented yourself. My alt prot pally is 8/14h(10 man obviously if i was a 25 tank id probably use tank cloak unless it was a aoe cleave fight) the cloak has 0 use on those bosses if you die you failed at using cds or mitigation at the right time. Maybe the later bosses it might but T15 4 set + DP is redic uptime on shield on heroics because of the dmg intake.