We wanted to give some the ability to have specific recipes that no one else may have, be it someone in a high end raiding guild or some random person that now has a unique purpose on his realm (until someone else discovers it of course).

Are they required for advancement or success as an Alchemist? Definitely not, but they're certainly a very nice perk if you happen upon one. The same could be said for world drop items, they're a nice perk, but in no way required for your character's advancement.

The randomness takes out the need to make the recipes so difficult to obtain that only the highest geared or most well supported alchemists have access.

Via WoW Forums (Europe)