Beyond - and perhaps more important than - his mere role as giant enemy crab, Paksigue represents an idea: There is something more powerful than you, and you must be on your guard or else you will be killed without the chance to really put up a fight. This idea of fear and challenge, of "there is something bigger than me," is why many of us play games in the first place. Who wants to feel like an invincible god all the time?
Crab Norris doesn't drop anything special; there are no phat lewts to be found. He is content that is meant to be bypassed - if you're aware of your surroundings and paying attention, you won't ever have to fight him. In this way, the idea of Crab Norris manages to fit neatly into the seemingly contradictory ideologies of "MMOGs should be easy and accessible for casual players" and "MMOGs need to give the hardcore players a challenge."
Since there is no positive incentive to fight the guy (nor any negative incentive for avoiding him), there is never any need for a casual player to try their hand at vanquishing a nigh-impossible foe - their progression won't be impeded in any way by their decision to play it safe. Similarly, the more adventurous players who decide to test their luck don't get an advantage over their more cautious cohorts. The idea of Crab Norris is like the idea of Mount Everest: You fight it because it's there.
In Aion, Crab Norris also serves as a bit of a wake-up call. His path is mostly random, and while there are still areas of relative safety where he won't patrol, he teaches newbie players to get used to checking their minimaps for that one red dot that's larger and moving more quickly than the others, as a driver might check their rear-view mirror. This is preparation for the later PvP-oriented stages of the game, where a large red dot means an enemy player who is just as deadly as any ferocious crustacean, whose movement is more random and who isn't bound by a maximum aggro radius.
The vicious beast might not have given us anything (virtually) tangible, but that's not to say we didn't come away from the fight the worse for the encounter. Defeating notorious foes that become infamous within a community lends itself neatly to a feeling of pride and satisfaction once all is said and done. We had vanquished Crab Norris, the scourge of Verteron Citadel. None would have to fear his deadly claws again (until he respawned). We were heroes!
That was a pretty damn good feeling, and it lasted quite a while ... until I was absentmindedly finishing a quest on my own, heard an ominous clatter of spindly legs, and was killed within a matter of seconds by a merciless foe exacting his revenge.
Damn you, Crab Norris!
John Funk doesn't sleep. He waits.