The idea is that instead of normal commands you give grouped units a Script Command(an AI script) which you wrote for the game(a set of scripts which automate micromanagement/player control).
1.select units
2.hold mouse at Script target Area(e.g. Attack center)
4.Press F1 -Script1,F2 Script2,etc
5.Units follow the script(script may have different tasks for a specific unit), as if the was played by computer.

Consistency:no errors
less stress:less micromanagement
faster command rate:execute complex sequences with 1 command
Automated Build Orders:perfect build order execution
More rich gameplay:players essentially design mini-programs to play against themself, doing all the dirty work(rapid clicking,micro-tactics, repeating tasks, resources management) and leaving the strategy to the player.