(possible spoilers) PSA: You can take travelers hub npcs into pretty much any area

Pretty much, if you ever find yourself in need of extra firepower or maybe just an extra teammate on your team, if you go to travelers hub and take on a quest where the quest giver goes with your team, you don't always have to go to their quest right away, they will follow you regardless of whether you are taking on their quest or not. As far as I can tell the only places they won't follow you are when you take a different quest or in the darkest lord battle.

This is extremely useful for post game battles like when you're trying to unlock the elf job, or fighting the dark sun. They can even follow you into the tower of dread!