Subing summoner but not using the actual skills gives a white mage a lot more mana for heals, buffs, and debuffs. The mana regen goes up as well. If you want to be a white mage and nothing more than summoner is a great sub. Watch out if you're a Taru because your hitpoints will be very low with no bonuses. if you use all the mana to spam heals you will die quickly.