Either that or that allows you to run say a split army. 2000 points of Marines, and 2000 points of Imperial Guard. While an opponent could have 2000 points of Dark Eldar and 2000 points of Biel-tan Eldar. On the next table someone has 2000 points of Vraksian Renegades and 2000 points of Emperor's Children versing another player with 2000 points of Feral Orks and 2000 points of Ork Kult of Speed. The combos could be wild. (I am guessing an allies table) say Tau and guard, but not tau and deathwatch.)
I suppose I am reminiscing of the old days when I had 15,000 points a side on a huge pair of table tennis tables with Eldar Orks and Nids versing Squats, Marines and Guard. The idea would make tournaments more interesting. The idea probably does not lend itself to balanced armies though. You could have enough Guard to fill out a marine army, add in the necessary artillery and tanks, and then use the Marines as a drop assault army to cripple the enemy.
I know the replies will have emoticons like
and so on.
I can only dream.