If the zombies have been given the tailed beasts back, it carries a big risk for Tobi to increase the count of missing beasts from two. But then again, it doesn't really matter if it's two or eight since he can't continue without all of them. However, for the allied forces snatching even one more away could be a nice bonus insurance against defeat.

But yeah, the six tails part was totally unnecessary. But since this is Naruto, the shounen filler king, it hardly surprised me.