PLD Clemency is so meh, there is nothing to hail about. Takes too long to cast (3s), costs a lot of MP and likely to get healed before done casting. Sure if there is downtime, but I rather be using hitting Royal Authority to do damage and keep hate. Better yet, be a pro PLD tank puller. Make the biggest pull early, plan to use Hallowed Ground as soon as you can to allow the healer to stay in-stance and get max dps, plus they can prepare whatever healing cooldown to use once it expires. Cooldowns will be back up later, and can even use again or 3x in some settings.