As Brett has pointed out already, the gist is that they run these scenarios at multiple locations in an effort to better achieve their goal: appeasing the sleeping god(s) for another year. Why risk failing with one when you can spread out your chances of success across multiple attempts?
What should be mentioned, though, is
The Cabin in The Woods is basically a critique of the horror genre in its entirety, and not just for American horror films but foreign ones as well. More recently the genre as a whole has been seen as dead; nothing is terribly scary anymore, too many horror movies rely on cheap jump moments, so everything has just sort of grown stale for many audiences.
The purpose of the other locations was to highlight this fact: even foreign markets haven't been able to "revive" the horror genre, to the point Whedon seems to feel they've failed outright. The way the Japanese team's scenario ends, with the little girls gathering around and singing a song to turn the demon into a frog, is Whedon's way of saying everything just ends up being cliche and formulaic.
As such, it's up to the Americans to come in and save the day, or at least that's what Whedon would have you believe.
Naturally the team in the US still fails, but the reason they fail is they still tried to stick to a "tried and true" formula. What happens, and what makes the movie truly pay off, is breaking the central characters out of the genre tropes and bringing them into the real world, along with the horrors that were saved for them in the fake one.
In the end Whedon had to destroy the world of horror films that's been built to forge a newer one, whatever that may be.