As you learn fights better, you will know exactly what you need your stacks for. For example, you might want to save one charge for sacred soil at a certain point in the fight, and you know this... but the others are yours to use however you like. For a reactive job like a healer, I would suggest that it is BETTER to save your stacks until your Aetherflow is ready to be used again, and then throw them off rather than overwriting/wasting them. That way, if you do need to use Lustrate in a pinch, you'll always have it ready to go (either because you saved them or because you are ready to use Aetherflow again).