"Min-Maxing" is a term that came to the MMO gamer from the pen and paper world, and is often spoken of in derisive tones. I don't really think this is fair; at its root, min-maxing is just another little puzzle-game that you play as part of the larger game. I thought I might step through the thought process that I went through with a few different upgrades, enchants, and gems yesterday and today to sort of show what's really going on when people talk about min-maxing.
To begin with, before I did a couple off-night tens last night, I happened to be exactly on hit cap using only Icewalker. Then I got a new necklace, the Sparkling Onyxia Tooth Pendant. The hit on the neck piece meant I was able to replace my Iron-Studded Mantle with the Pauldrons of the Devourer, which was good because those are the best shoulder items available right now, as far as I know.
The change did create a slight problem though: it put me four hit rating over the hitcap. At first I was going to leave it alone, since Icewalker is a slightly better enchant than Superior Agility. However, as I thought about it more, I realized that wasting 4 of those 12 points of hit was just too much. Especially because my new shoulders had a yellow socket with a 4 agility bonus on it! If I swapped Icewalker to the agility enchant, I would waste two less hit rating and get a four agility socket bonus I'd previously been missing. I made those changes earlier tonight and was glad to do it - I just feel better if I've gotten every point out of my gear that I can find in it, you know? And that's all min-maxing is: playing the little gear/enchant/gem puzzle game. Think of it like Bejeweled.