Every time I get tanking gear with a yellow socket, I cringe. Red socket? Get some agility. Blue socket? Get some stamina. But yellow socket? What do you get for that? +defense, +hit, or +crit. That's it for bear.
After doing all my defense math I hit up a guildie for Enchant Chest - Defense so I could remove my +13 worth of defense gems. Which was going to go great until I remembered that those defense gems were about the only good yellow gem option available for tanking. +6 stamina and +4 defense is nicely versatile for a yellow socket. The only other acceptable yellow alternative is +4 agility and +4 hit. But I can't afford to lose any stamina, and while the +hit is nice for threat I'm more worried about survival now.
Of course I can always blow off the socket bonuses and just fit whatever gems I want. But at the T4+ level the socket bonuses are quite good: +3 strength, +4 hit (half a gem itself!), etc. After all this work re-enchanting and regemming the best outcome is I have the same agility as before, +2 stamina, +4 hit, and -9 strength. That's not a win at all!