I can make it really easy for you.

Focus and target are the same thing EXCEPT
  • Target has default bindings to assign a mob/npc/player as target
  • Target is the default recipient for all targeted actions
Focus can be used to replicate all the actions of target with macros :)

so using targettarget in macros is the same as using focustarget

Pros of using focus:
  • It can't be accidentally changed through an accidental keypress
  • It frees up target to allow individual clones to retain specific targets (CC or DD etc)