You're right that except for healing potions, the others are pretty much optional. But they are useful at times, and sometimes they are really helpful. Especially things like Haste or Invisibility. They give you more options on progressing through the game, both in and out of combat. And having a hireling devoted to casting Longstrider at the beginning of the the day is a worthwhile thing on its own. That extra movement in combat is a godsend at times.
