Ever made an SMP and quickly found it lags a lot?
So we go to Chunky and we pregenerate our world. Then we remember the Nether and the End, and any modded dimensions (Blue Skies, Mythic Botany...) also need pregenerating!
OK, so let's pregen them all to, say, 2500 block radius. That's reasonable, right? Then we'll set a worldborder at 2000 block radius and it'll all be OK.
Lo and behold, there isn't enough End or Overworld. So we generate more of those dimensions, say 5000 block radius. Change the worldborder to 4500 radius.
Now we don't have enough world in the blue skies dimensions... and there's nothing stopping people from loading unloaded chunks in those dimensions, because the worldborder is the same in all dimensions!!
This mod allows you to manage your worldborders per-dimension through a new command:
/dimworldborder [dimension] [get/set/add...]
The original worldborder command remains, however it will only change the Overworld worldborder.
Bear in mind that (counterintuitively) the mod should be installed on both client and server. This is to prevent certain behaviour from occuring with players with high latency.