In the underdark if a player decides to explore the Beholder lair before entering Ust Natha they can get the Elder Orb eyestalk before it is needed. That's fine, as this can happen with lots of quests. But gaining the eyestalk triggers a journal entry saying you need to return to the Matron Mother. Since the party has not yet met the Matron Mother, this journal entry really ought not be posted. It would confuse a first time player, and is chronologically unpleasing to veteran players.
I assume the same thing would happen with the Mind Flayer lair.