Pls explain how early summoning spells are useful

[NTJedi]

Aleph said:
The Eater of the Dead starts out under your control, but, as you might guess from the name, he eats dead. This makes him stronger. After some amount of this (I have no idea what the corpse count has to be), he becomes an independent terror, running around attacking provinces at random. I think the main strat for him is to Gift of Reason him (IIRC he starts as a rank and file), load him up with nasties, and push straight into enemy territory. That way, when he goes bonkers, his rampages will still work out in your favor.

For 50 astral gems this creature has toooo many weaknesses to be considered worthwhile. Astral gems are more wisely spent on other summoning spells such as golem construction, juggernaut or ethergate.