One army is preferable, but if you work hard enough, you can still be of good use. The remaining company is of course the devil and possibly a threat to gaming itself.
It depends on the other army and situation.
You could be in the Nintendo army but hire yourself to do contract work for the Microsoft army if it meant discrediting the move or pointing out the 360 version of a multiplat game is better and or the Microsoft and Sony army can join forces to point out that the Wii is only for children and non-gamers.
Also, the Nintendo, Microsoft, and Sony amries can all join together to laugh at the PC army that still thinks they're relevant. :-p