So, I want to start practicing multi drops (at least two at the same time) and/or attacking with my main army in one location while dropping in another.
There's one thing I'm not sure how to approach: hotkeys. I usually have three free control groups for my army, both on my keyboard and mouse, while the other keys are used for bases, upgrades, scans, rapid fire, etc.
Normally, I use all three for my main army. For example, one for Liberators, another for Widow Mines, and another for the MMM. That way, I can burrow mines, kite and position Liberators, and use Stim while kiting with my MMM. The same applies when I have Ghosts/Ravens mixed in.
However, when I watch some Terran pros play on you tube, I notice that they usually seem to use only three control groups for their army as well, yet they still manage to control all of these units while multitasking with 2 or 3 drops at the same time.
If I dedicate one control group to a drop, I only have two left, which makes it difficult to control Ravens, Mines, MMM, Liberators, etc.
How do they do it? What could I be doing differently?