Sacrifice - how to use properly?

[bukimi]

I have sacrifice scroll and wonder if it is really worth learning.

I am barely on Verona and have over 20 intellect.
Still. On 3rd level it does only a bit more than 1000 damage.
That gives it only 500 health points of resurrecting power.
Even not enough to resurrect one dragon (or to create it).

Additionally, it can be cast only on own units. Which one should I sacrifice? Summoned by spell or from mystic egg?

I think that spell that expensive and also damaging own units should be more useful. Isn't it better to cast two damaging spells with the same amount of mana and hurt ENEMY?