Giving players more control over the unit level AI (i.e. how the unit responds in various circumstances or the set of instructions that it has) allows them to efficiently control a larger number of units. As real-time strategy has evolved many unit commands have been added. However, there's still room for expansion. An incomplete list:
Sequence of move coordinates/tasks
Patrol area
Patrol route
Don't move under any circumstances (hold position)
Move to engage enemy (x tiles) but return to position (don't move by more than y tiles)
Autoexplore
Hunt x unit types
When under attack by superior force, retreat to coordinates x,y