User blog comment:Braumissomanly/Whats with all the percentage damage?/@comment-8506165-20140822051429

Long story short: health is better than resists. Why? Both amplify your effective health, a blend is most optimal! Well... yes. However, only people building full tank have the luxury of building a lot of health and a lot of resists. For them it remains the most effective way to tank up. But for other people? Well, a blend is still the best for optimising your survivability... but resists protect you from only one of physical or magic damage. (True damage is only countered by health, as well - except Vayne's.) Without %health, though... well, you can just build a load of health (hence League of Warmogs) and be pretty damn unkillable. Ever been in a game where someone's built Warmog's and Mallet and your team have no % damage or items? Seen how hard it is to take them down? Yeah. Then they can just build offense.

So really, it's meant to keep bruisers in check. It does, however, have the unfortunate side effect of further diminishing the tank class, although I think    really doesn't help that either, becuase all those aforementioned items are still great for killing people with only average amounts of armor/MR so they're seen every game. Well, Youmuu's is only in some. But yeah. That combined with all the %health flying around makes it a lot harder to tank everything than it once was.