In SC2 you have multi building selection and you can select and group as many unit as you want under one hotkey. In SC:BW you can only select and hotkey one bui

In SC2 you have multi building selection and you can select and group as many unit as you want under one hotkey. In SC:BW you can only select and hotkey one building and unit groups are limited to 12 units. So you can have e.g. 36 units bind to keys 1-3 and 7 buildings bind to keys 4-0. Population cap in game is 200 and depending on game quite a lot of that cap will go to workers which you don't have to manage. That still leaves you with easily around 100 population or more of units that you have to micromanage. When you understand this watching somebody like Jaedong play zerg you'll understand how insane it is. He'll usually have hatcheries (buildings that build almost every zerg unit in the game) bind to 0-9 keys and then he'll manage and micro huge swarms of zerg units. Zerg are the quantity race in the game, you'll often have a ton of cheap units (e.g. zerglings or hydralisks) supplemented by few bigger units (ultralisks) and you have to manage them all (usually without keybinds), keep producing units, cast spells (using defilers) and do that all at around 400 apm (action per minutes) facing against another dude who is doing the same.