Anything you do in real time will benefit from repetition. If you need to consciously think about what you are doing, you may not have time to do it at all. If you can do it, you are performing suboptimally and probably focusing on your specific actions rather than incorporating them into a larger strategy.
When I started playing StarCraft II, I would refer to a friend who was jockeying to get into a diamond league, saying, “I don’t want to be that good.” Which is to say, I do not want to engage in the planning and repetition required to be that good. I am still thinking about my build order and looking around to see where ramps are on this map, rather than just building automatically and knowing the terrain.
You can think about only so many things at one time. If you think of your build order as a series of five steps, which you are working on while setting up your economy, you have about exhausted your mental resources. If you have played 1000 games and can subsume all of that under one mental unit of “Reaper rush,” you have lots of active attention available for strategizing and scouting. If you need to flip through three buildings and mouse-over some icons to find the research you want, you have lost time that your opponent has spent micromanaging his units. For him, it is practically Pavlovian to respond to the sound of an upgrade finishing and start the next level.
My early multi-player games were a series of constant re-discoveries of what things from the single-player campaign do not exist in multi-player play. I may not have played Zerg or Protoss as much, but at least I do not need to un-learn things to play those races. Except Scouts and Guardians from SC1, I miss those.