(This post is meant more for people who don't play World of Warcraft than those who do.)
One of the sick little pleasures of World of Warcraft is how much math there can be in the metagame of deciding your various strategies of how you're going to play. There are so many numbers that you can play around with.
The main character that I play in World of Warcraft is a healer when in large groups—out of a group of forty people, about a dozen are tasked with keeping the forty of us alive while the others kill our foes. Everyone has a number which represents how close or far they are from dying—their health. I have a number which represents how much magic power I have left to heal my friends—my mana. It regenerates more quickly if it's been five seconds since I've healed someone. I have various different spells at my disposal, all at different power levels. Each spell uses up a certain amount of my mana, takes a certain amount of time to cast, and restores a certain number of health points to my beneficiary. It's up to me to decide which spells are best used in each circumstance. If I choose the wrong ones, my friends may die because they're losing health points more quickly than I can restore them. If I choose the wrong ones, my friends may die because I've run out of mana points and can't cast any more spells to heal them. If I choose the wrong ones, my friends may die because a monster killed them in two seconds but that wasn't long enough for me to finish my healing spell.
But there's a lot more to it. The equipment that I'm wearing has a drastic effect on my abilities. I can put on equipment that gives me more health points or more mana points, or makes my mana regenerate more quickly, or makes each of my healing spells heal more points of damage for the same amount of mana. I don't get to just choose what I want; I have to deal with the equipment I've found, purchased, and earned in the game, and find the most optimal set of gear for every situation. Of course, I don't have to do those things, but it's a part of what separates a great healer from a good healer.
All of the math is very organic, because there are too many variables to pick an all-around best strategy, set of equipment, and complement of spells. I have to use instinct and my experience. It's a fun endeavor, tweaking numbers here and there to come up with new ideas on how I can more efficiently do my job in the game. I get to experiment with things to see how they work... it's a metagame—a game that takes place outside the real game. Building your deck in Magic: The Gathering is another metagame. I tend to like metagames because they give me an excuse to obsess about games.