OK, this is a little scary

[Niwde-blackrock]

Knowledge is power friend. Please read the rest of the AMA

@Kaivax

First, we’re absolutely committed to reducing to one layer per realm before our second content phase goes live, and the sooner we can get there, the better. The reason we can’t do that initially is that on launch day, everybody will be clustered in the starting zones, and having players so close together causes an exponential drain on server resources. In fact, the same number of players cause more server problems crammed into Northshire than they do spread across all of Elwynn Forest. We expect that even after the first couple of days, we’ll need fewer layers than we need for the initial hours of launch, and our stress tests have confirmed that expectation.

essentially its mostly for places where a mass amount of characters play.