By Lakshmi.Jaerik 2010-04-28 17:00:20
If you're curious about this, the MMO industry has formulae they use to establish the exact population per zone / area unit that is most ideal for retaining subscribers.
With a server that's too crowded, resources become too scarce and people become frustrated. But with a server that's not crowded enough, there aren't enough people to show off gear to, which is actually the most common reason people play. Without enough social acknowledgement of its worth, the gear loses its perceived value, and the game's motivation illusion falls apart.
It comes down to what's called density of "social interaction nodes," and it's a primary reason that MMO's have forced downtime where you can't move or do anything but talk / check people.
The ideal population coefficient is somewhere in between, and drives most of the design decisions in city layouts, expansions, mergers, and splits.