Crowd control

#showtooltip
/cast [target=mouseover, exists] Fear

This is useful in both PvE and PvP as it allows you to flexibly Fear an enemy without losing your target. Also, you should make a second Macro which replaces Fear and instead has Banish in it. It will look like this:-

#showtooltip
/cast [target=mouseover, exists] Banish

If you have a crowd control target you want to repeatedly Fear or Banish, your macro will look like this:

#showtooltip
/clearfocus [modifier:alt][target=focus,dead][target=focus,help][target=focus,noexists]
/focus [target=focus,noexists]
/cast [target=focus]Banish

Holding the ALT modifer when you press the button will reset your focus to your current target, helpful in situations where your CC target switches.