Are there situations where Damage Magicka/Regen or Damage Stamina/Regen is more effective than Damage Health?

I'm sure it's personal preference...

But i do carry the magicka based poisons. For me it's about crowd control. So, hagravens for ex will take an arrow first. W/o spells, I quickly dispatch the rest, then finish em off.

Well it depends on the npc you are fighting. When fighting mages you would want to use damage magicka and vice versa

How do you know when you've damaged all of an npc's magicka and magicka regen?

Is damaging magicka/regen significantly faster than killing the npc?