Mezz or Lull

[Malsivius]

been playing necro and rogue for too long because now that i'm dinking with bard and enchanter i am very confused (which is easy for having an oklahoma education) on how or which to use concerning Mezz or Lull.

to my ignorant brain, mezz seems better on keeping mobs out of engaging if their buddy is pulled next to them..so why would i use Lull?

thanks in advance