So, third character, might as well use the character boost so I can help my girlfriend through the story and level a new character, right? Right! Wrong. I used the character boost and now I can't access Warmind story missions because I haven't "unlocked" them. Excuse me, if I'm doing freaking Forsaken quest steps, shouldn't I be able to do the old stuff too? I know the character boost said I wouldn't be able to play them, ME. But they'd still be unlocked if I was with someone who was playing them. So what, if one daily story mission is from Osiris or Warmind I can't play that either? Zero, sense.
Using the boost skips all the story missions thus removing your ability to replay them (except as heroics)