"Well, they can't be all bad. Most of mine are pretty good, actually." Zack says.
OoC: Actually, the way Zack does limits and summons is via a trio of slots in a system called the Digital Mind Wave. Each one is unlocked by meeting a new person (like Cloud or Tseng) or picking up what is needed to summon them (like Materia or a chocobo Feather). In his final battle, as he slowly starts to weaken and die, it starts breaking. Each person in it starts to disappear and it starts to break. It's hugely symbolic.