I'm going to quote myself
Macro as a gaming technique is an application of economic theory; at its simplest it’s a distribution of limited resources between necessary avenues. Consider the simplest example from Starcraft: I have 50 minerals, I can purchase another worker to make minerals for me, or I can build an attack unit and go kill my opponent. The implied choice here is that I can trade an economic advantage (having and making minerals) for a tactical one (having units). Since winning usually requires a tactical advantage, at some point a player must make the decision: I’m going to sacrifice my economic advantage for a tactical one. To the uninitiated this may seem like an easy choice: I’ll just build attack units and destroy him if he’s building his economy. However, this sort of theory crafting doesn’t hold up. Once you consider things like: distance, time to kill, etc, you quickly realize that the person with the larger economic advantage can produce a larger army. How far away, and how long it takes to build an army are important factors in deciding between tactical vs economic advantage.
As if this tension between economic and tactical advantage was not sufficient, most RTS games introduce a third concept into Macro: Technology (or tech for short). Tech implies an investment of resources to produce better units. These units are conveying an advantage against your opponent at a smaller economic loss, even though they might be individually more expensive. The trade off between investing in tech and investing in economy is the same as economic vs tactical. Economic provides more units, where as tech provides better units. By comparison the trade off between tech and tactical is “how much more does this help vs building a new unit.”
These three forces are in constant tension not just in RTS games, but in the real world as well. Consider the Cold War era arms race. A nation could build Nuclear Submarines, Invest in its Infrastructure or build better Submarine detectors. Any one choice would give an advantage, but the reality is you have to invest in all three to remain competitive. This is known as the Red Queen Hypothesis, opponents must “run” as fast as they can, just to maintain status quo.
It is impossible to have a real discussion of Micro without first talking about Lim Yo-Hwan aka SlayerS_
BoxeR. Boxer first got his start in the South Korean bangs (lan centers) in the late 90s. It was in this environment that he demonstrated his skills. Micro comes from the word “Micromanagement,” the idea that if a player is talented or skilled enough he can individually direct every unit on the board. It was this property of Boxer that made him so popular. One of the reasons Starcraft draws so much attention as a sport is that it is more than just two players making strategic moves to out smart one another. There is an element of skill, of dexterity, that the better player might just be the one who plays better, not the one with better play.
At the core of Micro is that, no matter the unit composition or number, there is a way to have your units perform better than they should rightfully do. Through fast clicking and innate knowledge about unit strengths, Micro can mean the difference between losing all your Mutalisks to stimmed Marines, and rolling his army without a single loss. In some cases Micro is as simple as saying: Roaches have a short range, that means I should move closer than that range so the rank behind the first gets to attack; other times it’s things like: If I spread my Marines in 3 directions his Zealot will have to pick one and then walk a distance to the next; and very occasionally its: if I blink away my Stalkers who are at low health, I can save every one of my units while killing all of his.
Macro vs Micro
So why the yin yang? It seems like Macro and Micro are two things that every player needs. In a perfect world we’d all be 1000 APM pros who never broke a sweat; however, in the real world we are mere mortals who have to choose where they spend their attention. A person cannot concentrate on manipulating his force and strategize what he plans to do next, as the cost for task switching is very high for human beings. Instead we must strike a balance between these two ideas, and consider the opportunity cost inherent in both approaches. Ultimately you want to become good at both, but strike a balance between the two.