I sometimes use macros that change based on whether a target is friend or foe while using the same keybinding. Typically I use healing spells that are spammable that alternate with damage or CC spells that are also spammable.

For example, a shaman who wanted to cast Healing Wave on a target that is friendly or Lightning Bolt on a hostile target.

#showtooltip [help] Healing Wave; [harm] Lightning Bolt; Healing Wave

/cast Lifeblood

/cast [help] Healing Wave; [harm] Lightning Bolt

Notice the tooltip updates depending on your target hostility with the healing spell shown when the target is neither friendly or hostile or when you have no target. My shaman also happens to be a herbalist so I have lifeblood in there too. You can add trinkets to auto pop if you want.

Other examples of this macro type are as follows:

Purge a harmfull target of buffs or clense a friendly

#showtooltip [help]  Cleanse Spirit; Purge

/cast [harm] Purge; [help] Cleanse Spirit

I have a warrior and I use one button to charge a hostile target, intervene a friendly, or heroic leap with no target.

#showtooltip [help] Intervene; [harm] Charge; [@none] Heroic Leap

/cast [harm,exists,nomod] Charge; [help,exists] Intervene; [@none] Heroic Leap

Another macro I use to save some a button space is a interrupt macro. It skull bashes in cat or bear depending on what form I am in.

#showtooltip [stance:1] Skull Bash(Bear Form); [stance:3] Skull Bash(Cat Form)

/cast [stance:1] Skull Bash(Bear Form); [stance:3] Skull Bash(Cat Form)

I know there are mods for mounting but I have a macro that makes me fly if I can, ground mount if I can, cheetah if in combat, seal if I'm swimming with one button.

/cast [swimming] Aquatic Form(Shapeshift);  [flyable,nocombat] Swift Flight Form(Shapeshift);[nocombat] Golden King; Travel Form(Shapeshift)

If not a druid can change the macro to at least choose between a ground mount or flying mount like this.

#showtooltip [flyable] Violet Proto-Drake; Armored Razzashi Raptor

/cast [flyable] Violet Proto-Drake; Armored Razzashi Raptor

Then there are some abilitys that are off the global cooldown, my warrior uses a macro like this to maximize shield block uptime while in combat.

#showtooltip Devastate

/startattack

/cast Devastate

/cast [combat] Shield Block(Defensive Stance)