Hidden units for custom spells. Why?

I have just stumbled upon these trigger actions in the editor:
Unit-Damage target
and
Unit-Damage area

Do these actions completely replace the process of creating an invisible flying sheep and making it cast a spell for damage in trigerred spells, or is there a catch?

No catch. But you still need an invisible dummy unit for casting stuff in triggered spells, so it's not yet obsolete.

That just tells the unit to attack an unit/area. I thought everyone knew about that...

hey.. one question.. does damage area damage everything in that area including allies? how can i filter the target then without jass?