League of Legends

[Kaden]

What happens when you hit 160?

There's a system of diminishing returns on Armor and MR. You get more from Armor when you don't have very much, but less when you already have a bunch. Given the amount of gold that Armor items and HP items cost, you end up getting more defense for your money when you put it towards HP after you hit that ~160 threshold.

Of course, that doesn't mean that having more than that is dumb or worthless or whatever. If you had, like, 100 armor that doesn't mean that Thornmail (which gives you 100 Armor on its own) is suddenly an awful item. Could you more efficiently maximize your survivability if you used that same gold for something else? Probably, in a mathcraft kind of way, but that probably wasn't the point of buying the Thornmail in the first place.

Same thing goes for Randuin's Omen, Aegis of the Legion, Banshee's Veil, etc.. They all provide a lot more than the raw stats on the item. The diminishing returns thing is just something to keep in mind for those situations where all you care about is being as survivable as possible as efficiently as possible.