It's something like 2% difference in RNG mitigation from best to worst for tanks, in most cases people will have a mix and the difference will be 1% or less; in many other games the difference from BiS per slot and the next best thing is that 1% or greater making it much more worth it, but a possible 2% difference from the "perfect full set" of gear to the "worst full set" of gear is a bit daunting to strive for considering RNG factors on drops. I agree, if you can get it great, but don't expect it or be intimidated by content for not having it.
