The only times I ever find myself running low on mp is near the end of Titan and Garuda, both situations can get very intense and can require a lot of healing. So just ask the bard for balad, if he doesn't give it to you, the party wipes. Near the end of Titan the bard will probably always have balad up, simply because you can burn through 1-1.5k mp on the stomps. Being low on mp basically means you were doing your job correctly, or being a total idiot and just spamming succor all day and night when everyone is at full hp, shielded, and nothing is incoming while using aetherflow stacks to cast bane on a boss with no adds.