If someone is sitting in one ore a few similar factions, the lesser the probablility of him goofing something up on the other side of the barricade.
There's a damger however, that the status quo may change. Let's say, someone had two chars before the Tau war, 1 in KNF, another in BAF (hypothetical, our KNF ahs shown up when the war was already on), what then? Forced char deletion?