Defensive Stance, Guard, and Follow: What's the difference?

Break down of exactly how defensive stance, guard, and follow work. Guard, especially, has me thinking I should probably use it more often, but not for the reason I expected.
0:52 Unit behaviour on defensive stance
2:20 Changing the units' LOS
2:55 Retreating from archers
3:35 Defensive stance practical examples
4:00 Siege and demo ships
5:20 Guard
8:01 Guard "increases attack speed"
9:30 Self-guarding scouts
11:15 Follow
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Background music from Epidemic Sound: www.epidemicsou...
Game: Age of Empires II Definitive Edition