So I see a lot of people talking about how X% less damage helps your healers heal you X% less, but they still have to heal you. And in the current savage content, taking roughly, 7% less on an already mitigated (though CD's I would assume) "Critical Hit" from Halicarnasus at about 35k gives you around a 2.3k reduction. Your healer still needs to heal you for 32,700. Your roughly 1400 tenacity saved your healer less than half a GCD worth of healing potency, or a single GCD from the fairy.

In the case of auto attacks and sustained damage, now we're talking about even small value saved. Auto attacks doing 6k per hit, you mitigate 400 damage with a 7% reduction. Over 30 seconds (about 10 auto attacks), you've mitigated 4000 damage of that 60,000. In that same duration, your healer probably has 12 GCDs to spend. Your 1400 tenacity maybe saved your healer an oGCD directly on you, assuming there aren't already HoTs rolling on you or AoE healing being done to the party.