It exists to stop players killing any monster in the game with bio. Cast bio > logout > login with no aggro > cast bio > repeat till dead 4 hours later.
I remember trying to kill the RDM af3 ghost like this but it would always kill me before 30 seconds allowed me to logout.
Alternatively, you could take a monster to 50% HP then logout and log back in. call all fresh trusts wiht full HP and MP and go back to it.
It makes sense in battle ares, not towns.
