Ah, but there is also a negative side to the Trust system - for instance, if your NPCs die, you cannot resummon them if you have hate on you (in other words, you cannot resummon them in the middle of a battle, you have to summon them before engaging an enemy).

Also some of the healer npcs... aren't nearly as potent as they might seem to be (an example of this is Ferrous Coffin, the galka WHM from the Campaign battle system in the Wings of the Goddess expansion. Where as in Campaign his healing skills are extremely powerful, even being able to remove that annoying 'weakness' effect when raised... as a Trust npc.. he just... mostly hits enemies with the relic hammer Mjollnir and spams the weaponskill Randgrith, instead of healing like he should. You can also not heal your npcs yourself - hence if a healer npc runs out of MP (which they tend to do), that's all folks!

Still, it's an amazing system that definitely makes life so much easier - it's just not a complete replacement for actual players in a party.