Hi there! The dual purpose design here is the exert mechanics: it can make the game go faster, sending in more enemies so the boss will show up sooner, but will eat up unit turns which can make the swarms of enemies unmanageable. Also, it's always a matter of using them to make your shots hit more reliably, or relying fully on basic rolls to keep the number of enemies somewhat manageable - that is, if it actually hits at all before they swarm you yet again.