Spirits could not maintain their status as Spirit once they started to consume the Life Energy of other Spirits.
They would be unable to stop themselves from becoming corrupted by foreign energies that were not their own.
They would be able to absorb it for themselves but they would not be able to absorb it efficiently unless they ate something of a condensed that that could be absorbed more efficiently.
A lot of the Life Energy would be wasted during the absorption to make it their own.
If it was in a condensed state then smaller amounts could be broken down a little at a time without the energy going out of control and possibly causing troubles for the Spirit or escaping from the body when they lost control of it.
It was possible that those rampant energies could cause damage to their insides if not careful.
