OP, the simple answer is that creating and using good macros increases your ability to react quickly to events in game. This is the beginning and end of the discussion.
You want a warrior tank specific example? Here is a perfect example of why warrior tanks SHOULD be using macros.
You are tanking a boss. A paladin who meant to cast Blessing of Protection on a dps player accidentally casts it on you. This causes you to temporarily drop all threat, and you are unable to attack the mob until you locate the specific buff in your buff bar and right click to remove it. In the meantime, the mob is beating the crap out of your party. By the time you find the buff and right click to remove it, 2-3 of your raid members have died from being one-shot.
Instead of assigning Heroic Strike to your hotbar, you assign the following macro to your hotbar:
/cancelaura Blessing of Protection
/cancelaura Blessing of Salvation
/cancelaura Divine Intervention
#showtooltip
/cast Heroic Strike
Every time you hit this hotkey for heroic strike, you will automatically cancel Blessing of Protection, Divine Intervention, and Blessing of Salvation from your character if it is present, and you will use your chosen attack. So if a pally accidentally buffs you with an undesirable spell, you’ll dispel the effect before you even realize you had it. Copy this macro for sunder armor and any other ability you want to use while tanking, and suddenly you are 99% immune to trolling/sloppy paladins.
If I want to raid heal without macros (or addons), my movements look like this:
- Move mouse cursor to target needing healing.
- Mouse click.
- Press hotkey bind for healing spell.
- Move mouse cursor to next target needing healing.
- Mouse click.
- Press hotkey bind for healing spell.
While the amount of time between steps 2 and 3 can be extremely small, it must be present. If you have self-cast disabled in the game settings, those two steps can happen in either order, but there will always be a short delay between your two clicks.
With a mouseover macro, my movements look like this:
- Move mouse cursor over target needing healing.
- Hotkey bind for healing spell.
- Move mouse cursor to next target.
- Hotkey bind for healing spell.
Across the span of a long boss fight, this results in 33% less physical actions required of the player in order to do the same amount of work, which reduces mental fatigue. If you can perform a fast repetitive task in 2 steps or 3 steps, it is always better to perform it in 2 steps.
Another example:
As a paladin, there are times when I need to quickly bubble and then immediately drop the shield in order to clear a debuff. To do this manually, I must:
- Click the hotkey for Divine Shield.
- Move my mouse to the top right corner of my screen, locate the DS buff among all the other active buffs I have at the time, and right click to remove it.
With the following macro, all I have to do is tap a hotkey twice in rapid succession to achieve the same effect:
/cancelaura Divine Shield
#showtooltip
/cast Divine Shield
As a quality of life improvement, you can add /dismount to the start of all your attack macros so that you don’t have to manually keyboard/mouse click the keybind for your mount in order to attack a target. This can be of great benefit in busy areas that have players competing for tagging mobs, as you can be running towards a mob on your mount and tap your charge hotkey twice in rapid succession to instantly dismount and engage the mob.