How many units can you count? That is how many units you can micro.
Question answered, now for the background facts. This problem is the reason why multiple players can beat the same player: Even the most experienced of players can't count every unit on the battlefield... Maybe I can count 10 units per second, maybe an experienced player can count 300 units per second, but past that it becomes ridiculous, and that's just counting units and not actions taken. Zero-K often shows a ridiculous amount of not only units, but projectiles, resources... If we cannot count it all, we cannot control it. Sure, there are simplifications where you can, say, control a group, but a group is always dumber than the individual you count, and this still means that your control diminishes the more units you have to count. This is even funnier to think about, considering that the easiest way to resolve this fatal issue is to make more players, but the very goal of Zero-K is to make LESS players, making every point to win sound extremely dumb.
So, yeah, even in a game with rules as harsh as Zero-K, there is still a point in making company.