It stops the demons advance protecting thus the capital and delaying future demon attacks, but given how many lives were were lost (like 20k or something off the top of my head) it's hard to say it was worth it (not like Goddess actually cares though). Also had an unusual side effect that survivors/witnesses of the battle end up become friendly with each other forming a small human-demon town out of mutual fear of 'The Red Devil' (Makoto).